Route guidance system, information delivery center, and vehicular route guidance apparatus

ABSTRACT

An information center generates packets of route guidance information, each corresponding to a prescribed road length of a recommended route. The information center may generate major guide point information and guidance information and transmit both to a vehicular apparatus. The vehicular apparatus provides guidance only for major guide points based on the received major guide point information if it cannot receive the guidance information. According to another aspect of the invention, if the end of a route segment which was the subject of the preceding route guidance information is on an expressway or toll road, guidance information for a preliminary route from that end to an escape position ahead on the expressway or toll road is first transmitted and then information for a remaining route, that is a segment of the recommended route having the prescribed road length minus the preliminary route, is then transmitted. If communication with the information center is lost, the vehicular apparatus performs guidance for the preliminary route to an interchange, for example, of the expressway using the preliminary route guidance information.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a route guidance system andmethod for route guidance to a destination, to a related informationdelivery center, and to a vehicular route guidance apparatus. Morespecifically, the invention relates to a route guidance system in whicha vehicular route guidance apparatus having stored road data provides aguidance display for a route to a destination while in communicationwith an information delivery center also having road data, as well as tosuch an information delivery center and vehicular route guidanceapparatus.

[0003] 2. Description of the Related Art

[0004] In a conventional navigation apparatus that is provided in avehicle such as an automobile, when an operator has set a destination byoperation of an input section, a route from a detected present positionto the destination is searched for and route guidance is provided forthe thus determined route. The route is usually determined so as tominimize the distance to be covered from the present position to thedestination or to minimize the travel time.

[0005] In a conventional communication-type navigation system routeguidance is performed by communication between an information centerhaving road information and a navigation apparatus provided on a vehicle(Japanese Patent Laid-Open No. 19588/1998). In such a system, theinformation center reads necessary information from a database,responsive to a request from the vehicular apparatus, and generates amap image. The information center also generates information indicatingan optimum route by performing a route search. The generated map imageand information indicating the optimum route are sent from theinformation center to the vehicular apparatus and displayed on a displayof the vehicular apparatus.

[0006] In such systems, the configuration of the vehicular apparatus issimplified because the vehicular apparatus need not be equipped with adatabase. Since the database that is maintained in the informationcenter is updated frequently, route search results and map informationthat are generated based on the latest information can always besupplied to the operator.

[0007] However, because the map images and information for guidancealong an optimum route are communicated from the information center tothe vehicular apparatus, if the vehicle is running in an area wherecommunication cannot be performed properly or at all, e.g., when asystem is down or another problem arises in the information center,communication between the information center and the vehicular apparatusis interrupted and the vehicular apparatus cannot receive map images andinformation necessary for providing route guidance.

[0008] In a known navigation system that solves the problem, whencommunication between the information center and the vehicular apparatuscannot be performed, route guidance is continued by using mapinformation in a storage medium such as a CD-ROM or a DVD-ROM which isprovided in the vehicular apparatus (Japanese Patent Laid-Open No.2001-147132). However, if the map information stored in the storagemedium of the vehicular apparatus is old and the information center hasperformed a route search based on new information that is not includedin that map information, route guidance that is continued by using themap information stored in the storage medium of the vehicular apparatuswill be improper.

[0009] Assume a case wherein communication between the informationcenter and the vehicular apparatus is disabled in the middle of aguidance operation for an optimum route that was found by a route searchin the information center and includes a new expressway. In this case,the vehicular apparatus attempts to display a route based on thepreviously received information indicating the optimum route and usingthe map information stored in the storage medium of the vehicularapparatus. However, since the map information stored in the storagemedium of the vehicular apparatus has not been updated and thereforedoes not include the new expressway, the vehicular apparatus cannotdisplay a route including the new expressway on the display means. As aresult, the vehicular apparatus continues the route guidance bydisplaying a route including another, closest road such as an ordinaryroad, in place of the new expressway, and the route guidance becomesimproper. Further, the vehicular apparatus generates route guidanceinformation by performing map matching and a route search using the roaddata etc. stored in the recording medium. As a result, the vehicularapparatus displays a vehicle present position on the substituted closestroad that is recorded within the vehicular apparatus rather than on thenew expressway and performs route guidance from that misplaced presentposition.

SUMMARY OF THE INVENTION

[0010] The object of the present invention is to solve theabove-described problems. Accordingly, the present invention provides aroute guidance system (navigation system) capable of performing properguidance even in a situation wherein communication between a vehicularroute guidance apparatus and an information delivery center is notavailable and hence the vehicular route guidance apparatus cannotacquire route guidance information from the information delivery center.

[0011] According to one aspect of the invention, a navigation system isprovided which includes an information center having atransmission/reception section for communication, a route search sectionfor searching for a route, and an information generating section forgenerating major guide point information and guidance information forthe route thus found. The information center searches for an optimumroute based on a received present position and destination and generatesand transmits the major guide point information and the guidanceinformation. The navigation further includes a vehicular apparatushaving a transmission/reception section for performing communication, adestination setting section for setting a destination, a presentposition judging section for determining the present position, and aguidance output section for producing guidance output for major guidepoints and route guidance output for guidance along the route. Thevehicular apparatus serves to transmit the destination and the presentposition, to receive the major guide point information and the guidanceinformation, and to give guidance for the major guide points when unableto receive the guidance information.

[0012] In another aspect the present invention provides an informationcenter which has a transmission/reception section for communication; aroute search section for searching for a route; and an informationgenerating section for generating information for major guide points andguidance information for the route found by its search. The informationcenter searches for the route based on a present position and adestination that are received from a vehicular apparatus and generatesand transmits the information for the major guide points and guidanceinformation to the vehicular apparatus.

[0013] In yet another aspect the present invention provides a vehicularapparatus which includes a transmission/reception section forcommunication, a destination setting section for setting a destination,a present position determination section for determining a presentposition and a guidance output section for producing guidance output formajor guide points and route guidance output for guidance along theroute. The vehicular apparatus transmits the destination and the presentposition to an information center, receives, from the informationcenter, guide point information for major guide points and guidanceinformation for the route that has been found by a search based on thedestination and the present position, and gives guidance for the majorguide points when unable to receive the guidance information.

[0014] According to the present invention, even when the communicationbetween the information center and the vehicular apparatus has beendisabled, proper guidance can be performed by giving guidance for majorguide points.

[0015] According to still another aspect of the invention, a routeguidance system is provided which includes an information deliverycenter for generating route guidance information for route guidance froma present position to a destination in response to a request from avehicular route guidance apparatus and for transmitting the generatedroute guidance information to the vehicular route guidance apparatus.The information delivery center has search means for searching for aroute (“recommended route” or “guidance route”) from the presentposition to the destination, preliminary route guidance informationgenerating means for generating, if the guidance of a preceding routeguidance communication ended on an expressway or toll road, preliminaryroute guidance information for a preliminary route from that end to anexit position ahead, in generating route guidance informationcorresponding to a prescribed road length of the route that has beenfound by the search means. The information delivery center furtherincludes remaining route guidance information generating means forgenerating remaining route guidance information for a “remaining route”which is a segment of the recommended route having the prescribed roadlength minus the preliminary route; and transmitting means for firsttransmitting the preliminary route guidance information to the vehicularroute guidance apparatus and then transmitting the remaining routeguidance information to the vehicular route guidance apparatus. Thevehicular route guidance apparatus which provides the user with routeguidance, based on the route guidance information transmitted from theinformation delivery center, includes route guidance means for providingroute guidance for the recommended route ahead of the end of the routesegment for which complete guidance was last provided by transmissionfrom the information delivery center, in circumstances whereincommunication with the information delivery center is not possible, toan escape position for the expressway or toll road using the preliminaryroute guidance information that has been first received. According tothis aspect of the invention, when the communication between theinformation delivery center and the vehicular route guidance apparatusis disrupted and route guidance information for part of a toll road (orexpressway) ahead of the vehicle present position can not be displayed,preliminary route guidance is performed from that present position to anescape position ahead by using preliminary route guidance information.This can prevent improper route guidance wherein the vehicle presentposition would be displayed on the screen without that part of a newtoll road (or expressway) ahead of its position, for which guidance cannot be properly displayed, as in the case where the data for the newtoll road (or expressway) is not stored in the road data storing meansof the vehicular route guidance apparatus.

[0016] According to another aspect of the invention, an informationcenter is provided which, each time information for a present positionand a destination is received from a vehicular route guidance apparatus,generates route guidance information corresponding to a prescribed roadlength for route guidance from the present position to the destination,and transmits the generated route guidance information to the vehicularroute guidance apparatus. The information delivery center includessearch means for searching for a route from the present position to thedestination (“recommended route” or “guidance route”); preliminary routeguidance information generating means for generating, if an end of asegment of the recommended route (prescribed road length) covered by theimmediately preceding route guidance information is on an expressway ortoll road, preliminary route guidance information for a preliminaryroute from that end to an escape position ahead. The informationdelivery center also has remaining route guidance information generatingmeans for generating remaining route guidance information for a“remaining route”, i.e., a segment of the recommended route having theprescribed road length minus the preliminary route; and transmittingmeans for first transmitting the preliminary route guidance informationto the vehicular route guidance apparatus and then transmitting theremaining route guidance information to the vehicular route guidanceapparatus.

[0017] According to this aspect of the invention, if the end of a routesegment for which route guidance information is to be transmitted existson a toll road (or expressway), the information delivery centergenerates preliminary route guidance information for travel from thatend to an escape location ahead, and transmits the route guidanceinformation and the preliminary route guidance information together tothe vehicular route guidance apparatus. This operation can prevent thepreviously described improper route guidance.

[0018] According to still another aspect of the invention, a vehicularroute guidance apparatus is provided which receives, from an informationdelivery center, a series of transmissions separated in time, eachtransmission containing a packet of route guidance informationcorresponding to a segment of prescribed road length of the recommendedroute and provides route guidance to the destination using that routeguidance information responsive to each such transmission. The vehicularroute guidance apparatus includes route guidance information storingmeans for receiving, from the information delivery center, preliminaryroute guidance information, generated if the end of the segment of therecommended route covered by the preceding route guidance information ison an expressway or toll road, route guidance information correspondingto a prescribed road length, the preliminary route extending from thatend to an escape position ahead on the expressway or toll road. Eachsuch transmission further includes remaining route guidance informationfor a remaining route which is a segment of the recommended route havingthe prescribed road length minus the preliminary route. The vehicularroute guidance apparatus receives and stores both the route guidanceinformation and the preliminary route guidance information of eachcompleted transmission. The vehicular route guidance apparatus furtherincludes route guidance means for executing route guidance for arecommended route segment, when communication with the informationdelivery center is disrupted, from the end of the segment which was thesubject of the last complete transmission to an escape position on theexpressway or toll road, using only the received preliminary routeguidance information.

[0019] According to this aspect of the invention, the vehicular routeguidance apparatus receives route guidance information for a routesegment corresponding to a predetermined or set length of therecommended route and preliminary route guidance information to be usedwhen the end of the route segment corresponding to the predetermined orset road length falls on a toll road (or expressway), for guidance fromthat end to an escape position ahead on the expressway or toll road. Thereceived route guidance information and preliminary route guidanceinformation are stored in the route guidance information storing meansand the route guidance means performs route guidance based thereon. Thiscan prevent improper route guidance where the vehicle present positionwould be displayed without that part of the expressway or toll roadahead of the afore-mentioned end, when communication with theinformation center has been broken.

[0020] As used hereinafter “prescribed road length” is intended toinclude both a length set by the operator and a predetermined length.

[0021] According to a further aspect of the invention, a route guidancesystem is provided which comprises an information delivery center fortransmitting, to a vehicular route guidance apparatus, route guidanceinformation for route guidance to a destination, the informationdelivery center including search means for searching for a recommendedroute to the destination; and transmitting means for transmitting, tothe vehicular route guidance apparatus, route guidance information forguidance along the recommended route. The vehicular route guidanceapparatus provides route guidance based on the route guidanceinformation transmitted from the information delivery center, andincludes road data storing means in which road data is stored andre-search means for searching for a route again, using the stored roaddata, when communication with the information delivery center isunavailable and the vehicle has exited an expressway or toll road andentered onto an ordinary road.

[0022] According to this aspect of the invention, in the case where thevehicle is on an expressway when normal communication with theinformation delivery center is broken and the expressway is a newexpressway for which road data is not stored in the road data storingmeans, the re-search means of the vehicular route guidance apparatusdoes not perform a route search, using the road data contained in theroad data storing means, unless the vehicle first exits the expressway.Therefore, improper route guidance is not performed by substitution ofanother road, for which data is are stored in the road data storagemeans, for the new expressway.

[0023] In yet another aspect the present invention provides a method forcommunication of guidance information between a central informationcenter and plural vehicles each of which is equipped with a vehicularnavigation apparatus. This includes:

[0024] transmitting from the vehicular navigation apparatus to thecentral information center information identifying a present position ofa vehicle and a destination;

[0025] searching within the central information center, to determine arecommended route from the present vehicle position to the destination;

[0026] generating guidance information for the recommended route withinthe central information center;

[0027] transmitting the generated guidance information, as a series oftransmissions, to the vehicular navigation apparatus, each of saidtransmissions providing guidance information for a segment of therecommended route having a prescribed length, each of said transmissionsincluding a first portion of guidance information of short duration tobe utilized for guidance in the event of a failure in communicationbetween the central information center and the vehicular navigationapparatus and a second portion providing more detailed guidanceinformation for the route segment and having a duration significantlylonger than that of said first portion.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1 is a block diagram of a communication-type route guidancesystem according to a first embodiment of the present invention;

[0029]FIG. 2 is a time chart of operations of an information center anda vehicular apparatus of the route guidance system of FIG. 1;

[0030]FIG. 3 is a flowchart of a routine executed in operation of theinformation center of the route guidance system of FIG. 1;

[0031] FIGS. 4-8 are first to fifth flowcharts showing routines foroperation of the vehicular apparatus of the guidance system of FIG. 1;

[0032]FIG. 9 is a block diagram of a navigation system according to asecond embodiment of the invention;

[0033]FIG. 10 is a flowchart of a routine for route searching andguidance information transmitting within the information center of thenavigation system of FIG. 9;

[0034]FIGS. 11 and 12 are flowcharts of a routine for requesting androute guidance executed within the vehicular apparatus of the navigationsystem of FIG. 9;

[0035]FIG. 13 is a flowchart showing routine for receiving guidanceinformation executed within the vehicular apparatus of the navigationsystem of FIG. 9;

[0036]FIG. 14 is a flowchart of a routine for providing preliminaryroute guidance to the vehicular apparatus of the car navigation systemof FIG. 9;

[0037]FIG. 15 is a flowchart showing a requesting and route guidanceoperation of a vehicular apparatus according to a third embodiment ofthe invention;

[0038]FIG. 16 is a flowchart of a route guidance operation that isperformed in the vehicular apparatus when a communication problem hasoccurred, according to the third embodiment of the invention; and

[0039]FIG. 17 is a flowchart of a routine for route guidance executed bythe vehicular apparatus when normal communication with the informationdelivery center is not possible, according to a fourth embodiment of theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] Embodiments of the present invention will be hereinafterdescribed in detail with reference to the accompanying drawings.

[0041] Embodiment 1

[0042] As shown in FIG. 1, a first embodiment of the navigation systemof the invention includes a server 1 as an information center and avehicular apparatus 100 as a mobile navigation apparatus. Although thereactually exist a plurality of such vehicular apparatuses 100, forconvenience of description, in this embodiment they are represented bythe single vehicular apparatus 100.

[0043] The Server

[0044] The server 1 is a computer having a transmission/receptionsection 10, a computation section 20, a database 31, and an externalinformation collecting section 40. The server 1 may be asingle-apparatus server, a divided server in which a plurality ofapparatuses are combined together organically to function as a singleserver, as in a large server or computer.

[0045] Equipped with a communication device including a transmitter anda receiver, the transmission/reception section 10 communicates with thevehicular apparatus 100 over a network. The network may be a wired orwireless public communications network, a dedicated communicationnetwork, the Internet, an intranet, a LAN (local area network), a WAN(wide area network), a satellite communication network, a vehiculartelephone network, a cellular phone network, a PHS (personal handy-phonesystem) network, or a combination thereof. Communication may be bysatellite broadcast such as CS broadcast or BS broadcast, ground-wavedigital TV broadcast, or FM multiplex broadcast. Communication may alsobe by optical beacons or radio beacons which are installed alongsideroads and which transmit traffic congestion information,regulation-of-traffic information, etc.

[0046] The computation section 20 is equipped with a computing means 21such as a CPU or a MPU and a storing means 22 such as a semiconductormemory or a magnetic disk. The storing means 22 contains files ofvarious programs to be executed in the server 1. The files include aroute search program file 23 that contains a program for searching for aroute from a vehicle present position (e.g., a navigation start positionor a departure place) to a destination (i.e., a navigation endposition), a road length setting program file 24 that contains a programfor setting a road length indicating a range of guidance information tobe transmitted to the vehicle, a guidance information extracting programfile 25 that contains a program for retrieving guidance informationcorresponding to the road length that has been set by the road lengthsetting program and for editing the retrieved guidance information, acommunication judgment program file 26 that contains a program forjudging whether it is proper to transmit data, and a system controlprogram file 27 that contains a program for controlling and managing theentirety of the various operations. The storing means 22 also contains arequest road length information file 29 for storing information relatingto a route-search-requested road length, an extracted guidanceinformation file 30 for storing extracted route guidance information,and a major guide point information file 28 for storing information formajor guide points. Further, a working area to be used in executing anyof the above programs is included in the storing means 22. Configured asdescribed above, the computation section 20 functions as a route searchsection as well as an information generation section for generatingmajor guide point information and guidance information for a recommendedroute found by the search.

[0047] The database 31 contains files of information that are necessaryfor a route search and for route guidance. The files include a routesearch information file 32 that contains road network data etc., to beused in searching for a route to a destination, a guidance informationfile 34 in which route guidance information is accumulated, acommunication area information file 36 in which information relating tocommunication areas is accumulated, and a destination settinginformation file 38 that contains such information as telephone numbersand addresses for selection in setting a destination and locationscorresponding to those telephone numbers and addresses.

[0048] The route search information file 32 contains road networkinformation including information relating to intersections andinformation relating to nodes. The guidance information file 34 containsvarious items of guidance information such as map information coveringintersections and roads, landmark information indicating majorfacilities, and voice guidance information.

[0049] The communication area information file 36 contains informationrelating to communication states such as data to be used for determiningareas which radio waves cannot reach (non-communication areas), areasnot suitable for communication which only weak radio waves reach(communication-defective areas), and like areas. Thus, communicationareas can be determined by using this information.

[0050] The external information collecting section 40 is connected tothe database 31. The external information collecting section 40 is asection for updating the information stored in the database 31, asnecessary, using telephone lines or the like, latest road/trafficinformation and communication information such as traffic congestioninformation, traffic accident information, road constructioninformation, regulation-of-traffic information, information indicating anewly established road or facility, and changes in communication stateof a given area, e.g., change from a non-communication area to acommunication-defective areas. Each item of traffic congestioninformation, traffic accident information, road constructioninformation, regulation-of-traffic information, and informationindicating a newly established road or facility is collected in the formof a location and a date and time of occurrence and other information.For example, for traffic congestion information, a location and a dateand time of occurrence of a traffic jam and other information arecollected. The other types of information, such as traffic accidentinformation, are collected in similar manner.

[0051] The Vehicular Apparatus 100

[0052] The vehicular apparatus 100 includes a computing means such as aCPU or an MAU, a storing means such as a semiconductor memory or amagnetic disk, a display means such as a liquid crystal display, an LEDdisplay, or a CRT display, an input means such as a keyboard, a remotecontroller, or a touch panel, a communication interface, etc. Thevehicular apparatus 100 may be a cellular phone, a portable informationterminal, a PDA (personal digital assistant), a personal computer, avideo game machine, a digital TV receiver, or any other apparatus ofthis kind. In the preferred embodiment illustrated in FIG. 1 thevehicular apparatus 100 is a navigation apparatus provided in a vehiclesuch as an automobile, a truck, a bus, or a motorcycle, and includes acomputation section 101, a storing means 102, a position determinationsection 104 serving as a present position determination (judging)section, an input section 105 also serving as a destination settingsection, a display section 106 and a voice output section 107 serving asguidance output sections, and a transmission/reception section 108.

[0053] Equipped with a communication device including a transmitter anda receiver, the transmission/reception section 108 communicates with theserver 1 over the network. The computation section 101 has a computingmeans such as a CPU or an MAU. The storing means 102 has a semiconductormemory, a magnetic disk, or the like, and a program storage area 102Aand a data storage area 102B are contained in the storing means 102.

[0054] The program storage area 102A has a route guidance program file150 that contains a program for displaying a route and landmarks on thedisplay section 106 and for outputting voice route guidance from thevoice output section 107 based on route guidance information that istransmitted from the server 1. The program storage area 102A alsocontains a data request program file 152 that, in turn, contains aprogram for comparing a vehicle present position with received routeguidance information and requesting next route information and guidanceinformation, and a control program file 154 that contains a program forcontrolling the overall operation.

[0055] The data storage area 102B functions as a working area that isused as necessary in executing a program. Further, for example, the datastorage area 102B contains a route guidance information file 160 forstoring route guidance information that is transmitted from the server1, an ID information file 162 that contains a unique ID assigned to theassociated vehicular apparatus 100 for its identification, a vehicleposition information file 164 for storing vehicle position information(a longitude and a latitude) that is obtained by the positiondetermination section 104, and other files. The data storage area 102Bmay also store map information that is downloaded from the server 1 orsome other apparatus.

[0056] The vehicle position information file 164 stores, in addition topresent position data that is repeatedly obtained by the positiondetermination section 104 at a predetermined time interval, data of aplurality of past positions. For example, the vehicle positioninformation file 164 stores items of position information for points ona route of a predetermined distance that has been covered by the vehicleor items of position information for a predetermined number of points ona route that has been covered by the vehicle. When a new presentposition has been located by the position determination section 104, theresulting latest position information thus gathered is stored in thevehicle position information file 164 and the oldest positioninformation is erased from it. A running locus of the vehicle can beobtained by connecting the positions represented by items of positioninformation stored in the vehicle position information file 164. Therunning locus is used for map matching to identify the road on which thevehicle is running.

[0057] The position determination section 104 is a section thatdetermines a vehicle position using the GPS (global positioning system)etc., and is equipped with a GPS receiver for determination of a vehicleabsolute position from signals received from a plurality of GPSsatellites and is further equipped with a speed sensor, a directionsensor, etc., for determination of a vehicle relative position. Thespeed sensor and the direction sensor may be used for independentnavigation. A relative position that is determined based on signals fromthese sensors is used for determining a vehicle position in a tunnel,for example, where the GPS receiver cannot receive radio waves from GPSsatellites or correct for a measurement error in an absolute positionthat is measured by the GPS receiver. Where the vehicular apparatus 100is a cellular phone, a portable information terminal, or the like, theposition of a base station that covers a range where that vehicularapparatus is located is detected as a present position throughcommunication with the base station.

[0058] The input section 105 includes various switches, a touch panelthat is attached to the display screen of the display section 106, aremote controller, a speech recognition data input device, etc. When theuser touches the touch panel with his finger at an icon or the likedisplayed on the display section 106, a corresponding instruction oritem of information is input. The speech recognition data input devicerecognizes the voice of the operator, whereby a correspondinginstruction or data is input.

[0059] The display section 106 is a liquid crystal display, a CRTdisplay, or the like. It is desirable that the display section 106 beequipped with the above-mentioned touch panel.

[0060] The transmission/reception section 108 communicates with theserver 1 over the network.

[0061] The vehicular apparatus 100 preferably is equipped with a routesearch program, route search information, guidance information,destination setting information, etc. and has the ability to, forexample, perform a route search and generate guidance informationwithout communicating with the server 1. If this is the case, theoperator can choose either the server 1 or the vehicular apparatus 100as the apparatus that to perform part or all of such operations asdestination setting, route searching, and generation of guidanceinformation.

[0062] Next, operations of the communication-type route guidance systemhaving the above configuration will be described with reference to FIGS.2 and 3.

[0063] First, the operator, e.g., driver of the vehicle, sets adestination and inputs an instruction to search for a route to thedestination by use of the input section 105 of the vehicular apparatus100. In response, as indicated by symbol F1 in FIG. 2, the vehicularapparatus 100 transmits, to the server 1, information such as a vehiclepresent position, as located by the position determination section 104,and the destination, as well as a request for performing a route searchand sending back search results and guidance information. At the sametime, the vehicular apparatus 100 transmits ID information to be usedfor distinguishing the vehicular apparatus 100 from others. Thecommunication between the vehicular apparatus 100 and the server 1 ispacket communication, for example.

[0064] In the server 1, the request from the vehicular apparatus 100 isreceived by the transmission/reception section 12 and supplied to thecomputation section 20. In the computation section 20, the request isreceived and the computing means 21 performs a route search by executingthe route search program that is stored in the storing means 22. Morespecifically, first, as indicated by symbol F2 in FIG. 2, a vehiclepresent position and a destination are extracted based on the receivedinformation. For example, if such information as a telephone number oran address is received as the destination information, a destination isextracted by using the destination setting information file 38 that isstored in the database 31.

[0065] Then, information relating to a road length that is included inthe received information is stored into the request road lengthinformation file 29 and a route from the vehicle present position to thedestination is searched for. The road length may be properly set in theserver 1. The route search is performed by referring to the route searchinformation that is stored in the database 31, that is, the intersectioninformation, the road information, and the node information. The routesearch operation itself is a known technique. A recommended route is setin accordance with prescribed conditions such as an instruction that theroute whose entire length is shortest be made the optimum (“designated”or “recommenced”) route (refer to Japanese Patent Laid-Open Nos.173297/1989 and 173298/1989).

[0066] In this embodiment, a route from a vehicle present position tothe destination is searched for each time a request is received from thevehicular apparatus 100. In the server 1, the external informationcollecting section 40 acquires road information and traffic informationfrom external sources and the contents of the database 31 are updated toinclude the latest information. Therefore, by performing a route searchevery time a request is received from the vehicular apparatus 100,traffic jam locations, road construction locations, accident locations,and the like can be avoided and hence a recommended route that reflectsthe latest data and corresponding guidance data can always be suppliedto the vehicular apparatus 100.

[0067] Then, guidance information that is associated with a rangecorresponding to the road length is retrieved by referring to theguidance information file 34 of the database 31 by executing theguidance information extracting program that is stored in the storingmeans 22. As indicated by symbol F3 in FIG. 2, the route information andthe guidance information are transmitted to the vehicular apparatus 100by the transmission/reception section 10.

[0068] Next, as indicated by symbol F4 in FIG. 2, the vehicularapparatus 100 provides guidance for a length of the route correspondingto the set road length as display on the display section 106 and/orvoice output from the voice output section 107. When the vehicle hascovered a distance corresponding to the set road length and guidanceinformation for continued guidance for the route ahead (i.e.,“continuation route guidance information”) has become necessary, thevehicular apparatus 100 again transmits, to the server 1, informationsuch as a vehicle present position and the destination as well as arequest for performing a route search and sending back search resultsand guidance information based on the search results, as indicated bysymbol F5 in FIG. 2.

[0069] In response, the server 1 repeats the above-described operationsand transmits route information and guidance information correspondingto an additional (“continuation”) road length to the vehicular apparatus100. From this time onward, the above-described operations are repeatedas shown in FIG. 2 until the vehicle reaches the destination or theoperator inputs, to the input section 105, an instruction to stop thenavigation.

[0070] The server 1 may continue to store a route that was found inresponse to a first request from the vehicular apparatus 100 andtransmit guidance information that is extracted based on the storedroute when continuation route guidance information becomes necessary.This decreases the number of route searches and hence reduces the loadon the server 1. Since guidance information is transmitted in divisions(“segments”) of the recommended route, each division having the set roadlength, the time required for one communication is shortened. If it isjudged, based on a received present position, that the vehicle hasdeparted from the recommended route, the server 1 again performs a routesearch to find a new route.

[0071] Next, the operation of the server 1 will be described withreference to the flowchart of FIG. 3.

[0072] Step S1: the server 1 waits until a request for route informationand guidance information is received from the vehicular apparatus 100.If a request is received, the routine goes to step S2.

[0073] Step S2: The server 1 extracts vehicle present positioninformation and destination information.

[0074] Step S3: The server 1 searches for a route from the presentposition to the destination.

[0075] Step S4: The server 1 retrieves guidance informationcorresponding to a prescribed (e.g., “set”) road length.

[0076] Step S5: The server 1 transmits route information and guidanceinformation to the vehicular apparatus 100.

[0077] Next, the operation performed by the vehicular apparatus 100 whenit cannot receive guidance information from the server 1, because of anabnormal break in communication between the server 1 and the vehicularapparatus 100, will be described with reference to FIGS. 4-8.

[0078] First, the operator, e.g., the driver of the vehicle, sets adestination and inputs an instruction to search for a route to thedestination by use of the input section 105 of the vehicular apparatus100. It is desirable that the operator be able to set conditions for thesearch. For example, the operator may specify that expressways shouldaccount for as large a part of the route as possible, that ordinaryroads should account for as large a part of the route as possible, thatthe route should require the minimum expense possible, or that cityroads should account for as small a portion of the route as possible.

[0079] Then, by use of the input section 105, the operator makes aselection which determines whether the vehicular apparatus 100 performsthe route search or the server 1 performs the route search. For example,where the route search by the server 1 or the communication between theserver 1 and the vehicular apparatus 100 requires payment of a fee, theoperator may elect to have the route search conducted by the vehicularapparatus 100 if he wants to save the expense. Where the server 1 hasthe latest map information, road network information, etc., while thevehicular apparatus 100 does not, the operator may select a route searchby the server 1 if he wants to receive a result and guidance informationbased on the latest information. Where the vehicular apparatus 100 doesnot have a route search function, the operator cannot have the vehicularapparatus 100 perform a route search and hence he can only have a routesearch conducted by the server 1.

[0080] The vehicular apparatus 100 need not always have map information,guidance information, and destination information. Where the vehicularapparatus 100 does not have such information, the operator cannot causethe vehicular apparatus 100 to perform a route search and hence heselects a route search by the server 1.

[0081] If the operator has selected a route search by the vehicularapparatus 100, the vehicular apparatus 100 starts a search and theposition determination section 104 locates the vehicle present position.Then, a route from the present position to the set destination issearched for and the result is stored in the storing means 102. Then,guidance information for the route thus found, for example, informationrelating to a right or left turn at an intersection, a lane changebefore a branching point, or entrance into an interchange of anexpressway, is generated and stored in the storing means 102.

[0082] If the operator has selected the server 1 to conduct the routesearch, the vehicular apparatus 100 transmits, to the server,information necessary for a search such as a vehicle present positionand a destination, ID information, information relating to a roadlength, and other information, as well as a request for performing aroute search and sending back the results and guidance information forguidance along the route found. In response, as described above, theserver 1 performs a route search and sends back the route found (i.e.,“recommended route”) to the vehicular apparatus 100.

[0083] Further, the server 1 extracts guidance information for the routefound and transmits the extracted information to the vehicular apparatus100. This is done in the following manner. First, the vehicularapparatus 100 transmits, to the server 1, a request for sending backinformation for major guide points. The major guide point information isinformation relating to major guide points on the recommended route.Where the route includes an expressway or a toll road, examples of themajor guide points are entrances to the expressway or toll road, in theform of interchanges and junctions, service areas, parking areas andexits in the form of interchanges and junctions. Where the routeincludes a road such as a bypass or a bridge that the vehicle cannotenter or exit, examples of the major guide points are intersections atthe entrance and the exit of the road.

[0084] Receiving the request for sending back major guide pointinformation, the server 1 extracts major guide point information andtransmits it to the vehicular apparatus 100. In this manner, thevehicular apparatus 100 can acquire the major guide point information.Each piece of major guide point information includes, for example,coordinates, name, attribute (interchange, junction, service area,parking area, intersection, passage point, destination, or the like),road name, road type (intercity expressway, city expressway, toll road,ordinary road, or the like), image data, voice data, area information,and facility name.

[0085] At this stage, the vehicular apparatus 100 judges whether it hassucceeded in receiving all the major guide point information. If thevehicular apparatus 100 judges that it has not received the major guidepoint information completely (because of some problem incommunication—an “abnormal communication state”), the vehicularapparatus 100 recognizes that display of an alarm is needed. Forexample, an abnormal communication state occurs when the vehicle isrunning in a non-communication area or a communication-defective area,when the state of the ionosphere is unstable, and when one of thesystems in the network is down.

[0086] Next, the vehicular apparatus 100 transmits a guidanceinformation request to the server 1. Receiving the guidance informationrequest, the server 1 retrieves guidance information corresponding tothe set road length and transmits it to the vehicular apparatus 100. Inthis manner, the vehicular apparatus 100 can acquire the guidanceinformation corresponding to the road length and store it in the storingmeans 102.

[0087] If the guidance information includes all or part of the majorguide point information, the server 1 may delete that portion of themajor guide point information that has already been transmitted to thevehicular apparatus 100 from the guidance information to be nexttransmitted. In this manner, the amount of information to be transmittedcan be reduced and the time required for transmission can be shortened.

[0088] The system may be so configured that the server 1 transmits majorguide point information and guidance information to the vehicularapparatus 100. In this case, the server 1 automatically transmits majorguide point information and guidance information to the vehicularapparatus 100 upon receiving a present position, a destination, etc.from the vehicular apparatus 100.

[0089] At this stage, the vehicular apparatus 100 judges whether it hassucceeded in receiving the complete guidance information. If thevehicular apparatus 100 judges that it has not received the guidanceinformation completely because of a some abnormal state ofcommunication, the vehicular apparatus 100 recognizes that an alarmdisplay is needed and that guidance for the major guide points needs tobe generated.

[0090] When the vehicular apparatus 100 has generated or received theguidance information and has stored it in the storing means 102, theoperator inputs an instruction to start guidance, that is, requests astart of guidance, by use of the input section 105. In response, theposition determination section 104 updates the location of the vehiclepresent position. Based on the updated present position, the vehicularapparatus 100 judges whether to update the guidance information that isstored in the storing means 102. The guidance information is updatedwhen the vehicle has covered a distance corresponding to the set roadlength after the previously generated or received guidance informationwas stored in the storing means 102 and new guidance information forguidance for a route ahead (i.e., continuation guidance information) hasbecome necessary.

[0091] If judged that the guidance information need not be updated, thevehicular apparatus 100 acquires, as information to be provided asguidance, the previously generated or received guidance information thatis stored in the storing means 102.

[0092] On the other hand, if judged that the guidance information needsto be updated, the vehicular apparatus 100 generates or receives newguidance information. More specifically, the vehicular apparatus 100judges whether the route search was performed by the vehicular apparatus100 or by the server 1. If the route search was performed by thevehicular apparatus 100, the vehicular apparatus 100 generates newguidance information in the same manner as described above. If the routesearch was performed by the server 1, the vehicular apparatus 100receives new guidance information from the server 1 in the same manneras described above. The vehicular apparatus 100 stores the new guidanceinformation in the storing means 102 and retrieves it as guidance.

[0093] Then, the vehicular apparatus 100 judges whether it has succeededin acquiring information to be provided as guidance, that is, whetherthere exists information to be provided as guidance. If there existsinformation to be provided as guidance, the vehicular apparatus 100outputs route guidance in the form of route display on the displaysection 106 and/or voice output from the output section 107.

[0094] On the other hand, if there exists no information to be providedas guidance, the vehicular apparatus 100 judges whether an abnormalstate of communication exists. If an abnormal state of communication isjudged, the vehicular apparatus 100 judges whether it is necessary toprovide guidance for the major guide points.

[0095] If it is necessary to provide guidance for the major guidepoints, first, the vehicular apparatus 100 acquires the present positioninformation. The vehicular apparatus 100 then judges whether the vehiclehas passed the first major guide point. If the vehicle has not yetpassed the first major guide point, the vehicular apparatus 100 acquiresinformation relating to the first major guide point. A judgment that thevehicle has passed the first major guide point is made if the vehiclehas entered and then exited a circular area that is centered on thefirst major guide point and has a prescribed radius (e.g., 300 m). Ifthe vehicle has passed the first major guide point, it is then judgedwhether the vehicle has passed the second major guide point. Afterconfirming that information relating to the first major guide point hasbeen acquired, the vehicular apparatus 100 repeats the above operationfor the second major guide point and so on, for the remaining majorguide points. The vehicular apparatus 100 then displays, on the displaysection 106, the guidance information for the major guide points and analarm message indicating a failure to receive guidance information fromthe server. Alternatively, the guidance information for the major guidepoints and the alarm message may be output from the voice output section107. If no information relating to the major guide points can beacquired, a message to that effect is also displayed.

[0096] Assume a case that a route includes an expressway and first tothird major guide points are an interchange at which to enter theexpressway, a service area to be passed on the expressway, and aninterchange at which to exit the expressway, respectively. If thevehicle is traveling on the expressway, that is, if the present positionis on the expressway, the vehicular apparatus 100 judges that thevehicle has passed the entrance interchange and judges whether thevehicle has passed the service area without acquiring informationrelating to the entrance interchange. Then, if the vehicle has notpassed the service area yet, the vehicular apparatus 100 acquiresinformation relating to the service area as well as information relatingto the interchange at which to exit the expressway. The vehicularapparatus 100 displays, on the display section 106, a message to theeffect that route guidance cannot be performed due to an abnormal stateof communication, and gives guidance to the effect that the vehicleshould exit the expressway at the exit interchange after passing theservice area.

[0097] After giving guidance for the present position or displaying thealarm message and giving guidance for the major guide points, thevehicular apparatus 100 judges whether an instruction to stop theguidance has been input or the vehicle has reached the destination. Ifan instruction to stop the guidance has been input or if the vehicle hasreached the destination, the vehicular apparatus 100 finishes the routeguidance operation. On the other hand, if an instruction to stop theguidance has not been input and the vehicle has not yet reached thedestination, the vehicular apparatus 100, updates the present positionand repeats the above-described operation.

[0098] The system may be so configured that the vehicular apparatus 100gives guidance for the major guide points even if there is no problem incommunication with the server. In this case, the operator can recognizethe major guide points in advance and hence can reach the major guidepoints easily even if a problem with communication subsequentlydevelops.

[0099] The system may be so configured that when the present position ison an expressway, a toll road, or an upper level of a multi-level road,the server 1 transmits information relating to an interchange at whichto exit the expressway, toll road, or upper level of the multi-levelroad to the vehicular apparatus 100 as major guide point information. Inthis case, when a problem with communication (“abnormal communicationstate”) has occurred during the vehicle's travel on an expressway, atoll road, or a high level of a multi-level road, the operator caneasily recognize the interchange at which to exit the expressway, tollroad, or upper level layer of the multi-level road.

[0100] Further, the system may be so configured that the server 1transmits information relating to the interchange at which to exit theexpressway, toll road, or upper level of the multi-level road to thevehicular apparatus 100 as major guide point information, irrespectiveof the present position, if the end of the section of theabove-mentioned set road length is located on the expressway, toll road,or upper level of the multi-level road. In this case, even if thevehicle present position is on an ordinary road leading to theexpressway, toll road, or upper level of the multi-level road and aproblem with communication later develops, the operator will be able toeasily recognize the interchange-at which to exit the expressway, tollroad, or upper level of the multi-level road.

[0101] Next, the routines of the flowcharts of FIGS. 4-8 will bedescribed.

[0102] Step S11: The operator sets a destination by use of the inputsection 105 of the vehicular apparatus 100.

[0103] Step S12: The operator sets a search condition.

[0104] Step S13: The operator chooses between a route search by theserver 1 and a route search by the vehicular apparatus 100. The processgoes to step S17 if a route guidance by the server is selected, and tostep S14 if a route guidance by the vehicular apparatus 100 is selected.

[0105] Step S14: The vehicular apparatus 100 starts a route search.

[0106] Step S15: The vehicular apparatus 100 acquires the searchresults.

[0107] Step S16: The vehicular apparatus 100 generates guidanceinformation.

[0108] Step S17: The vehicular apparatus 100 transmits informationnecessary for a search and requests the server 1 to perform a routesearch.

[0109] Step S18: The vehicular apparatus 100 receives the searchresults.

[0110] Step S19: The vehicular apparatus 100 receives guidanceinformation.

[0111] Step S19-1: The vehicular apparatus 100 transmits, to the server1, a request for sending back major guide point information.

[0112] Step S19-2: The vehicular apparatus 100 acquires major guidepoint information.

[0113] Step S19-3: The vehicular apparatus 100 judges whether thevehicular apparatus 100 has successfully received all the major guidepoint information. The process goes to step S18-5 if the vehicularapparatus 100 has succeeded in doing so, and to step S19-4 if not.

[0114] Step 19-4: The vehicular apparatus 100 judges that an alarmdisplay is necessary.

[0115] Step S19-5: The vehicular apparatus 100 transmits, to the server1, a request for sending back guidance information.

[0116] Step S19-6: The vehicular apparatus 100 receives guidanceinformation from the server 1.

[0117] Step S19-7: The vehicular apparatus 100 judges whether it hassuccessfully received all the guidance information. If the vehicularapparatus 100 has not succeeded in doing so, the process goes to stepS19-8.

[0118] Step S19-8: The vehicular apparatus 100 judges that an alarmdisplay is necessary.

[0119] Step S19-9: The vehicular apparatus 100 judges that display ofmajor guide points is necessary.

[0120] Step S20: The vehicular apparatus 100 receives a guidance startrequest.

[0121] Step S21: The vehicular apparatus 100 updates the presentposition.

[0122] Step S22: The vehicular apparatus 100 judges whether it isnecessary to update the guidance information. The process goes to stepS23 if it is necessary to do so, and goes to step S24 if not.

[0123] Step S23: The vehicular apparatus 100 generates or receives newguidance information.

[0124] Step S23-1: The vehicular apparatus 100 judges whether the routesearch was performed by the server 1. The process goes to step S23-3 ifthe route search was performed by the server 1, and goes to step S23-2if not.

[0125] Step S23-2: The vehicular apparatus 100 generates new guidanceinformation.

[0126] Step S23-3: The vehicular apparatus 100 receives new guidanceinformation (as in step S19).

[0127] Step S24: The vehicular apparatus 100 acquires the guidanceinformation that is stored in the storing means 102.

[0128] Step S25: The vehicular apparatus 100 judges whether there existsinformation to be provided as guidance. The process goes to step S27 ifsuch information exists, and goes to step S26 if not.

[0129] Step S26: The vehicular apparatus 100 judges whether a state ofabnormal communication state exists. The process goes to step S28 ifthere is an abnormal communication state, and goes to step S27 if not.

[0130] Step S27: The vehicular apparatus 100 gives guidance for thepresent position.

[0131] Step S28: The vehicular apparatus 100 judges whether guidance forthe major guide points is necessary. The process goes to step S29 ifguidance for the major guide points is necessary, and goes to step S30if not.

[0132] Step S29: The vehicular apparatus 100 gives guidance for themajor guide points.

[0133] Step S29-1: The vehicular apparatus 100 acquires present positioninformation.

[0134] Step S29-2: The vehicular apparatus 100 increments the majorguide points.

[0135] Step S29-3: The vehicular apparatus 100 judges whether the majorguide point has been passed. The process returns to step S29-2 if themajor guide point has been passed, and goes to step S29-4 if not.

[0136] Step S29-4: The vehicular apparatus 100 acquires major guidepoint information.

[0137] Step S29-5: The vehicular apparatus 100 judges whether the majorguide point information has been received. The process goes to stepS29-6 if the major guide point information has not been received.

[0138] Step S29-6: The process goes to the next step if steps S29-2 toS29-5 have been repeated for all the major guide points.

[0139] Step S30: The vehicular apparatus 100 displays an alarm message.

[0140] Step S31: The vehicular apparatus 100 judges whether it hasreceived an instruction to stop the guidance or the vehicle has reachedthe destination. The process is finished if the vehicular apparatus 100has received an instruction to stop the guidance or the vehicle hasreached the destination. Otherwise, the process returns to step S21.

[0141] Steps S12, S14 to S16, S19-1, S19-3 to S19-5, S19-7 to S19-9,S20, S23-1 and S23-2, S25, S28, S29-1 to 29-6, S30, etc. may be omittedas necessary.

[0142] As described above, in this embodiment, the navigation systemincludes the server 1 and the vehicular apparatus 100. The server 1performs a route search and the vehicular apparatus 100 can receive andoutput a search result and guidance information for the route found bythe server 1. Further, the vehicular apparatus 100 can acquire majorguide point information. Therefore, even when an abnormal state ofcommunication prevents the vehicular apparatus 100 from receiving routeguidance information from the server 1, the vehicular apparatus 100 cangive guidance for major guide points and hence the operator can acquirea minimum amount of guidance for the route. Therefore, the vehicularapparatus 100 need not continue the route guidance using map informationetc., which it has stored, and can avoid improper guidance.

[0143] Assume a case wherein communication between the server 1 and thevehicular apparatus 100 is disabled in the middle of a guidance for anoptimum route that was found by a route search in the server 1 andincludes a new expressway and wherein, as a result, the vehicularapparatus 100 can no longer acquire guidance information for the routeahead from the server 1. In this case, in the conventional navigationsystem previously described in the “BACKGROUND OF THE INVENTION”section, the vehicular apparatus attempts to display guidanceinformation for the route ahead on a map, based on the previouslyreceived data of the optimum route, using the map information stored inthe storage medium of the vehicular apparatus. However, if the mapinformation stored in the storage medium of the vehicular apparatus hasnot been updated, it may not include the new expressway and hence thevehicular apparatus cannot display a route including the new expresswayon the map. As a result, the vehicular apparatus continues the routeguidance by displaying a route including an ordinary road in place ofthe new expressway on the map and the route guidance therefore becomesimproper.

[0144] In contrast, in the navigation system according to the presentinvention, the vehicular apparatus 100 receives at the outset, as majorguide point information, guidance information for an interchange atwhich to enter an expressway, a service area to be passed in travel onthe expressway, and an interchange at which to exit the expressway.Therefore, even if communication between the server 1 and the vehicularapparatus 100 is disabled while the vehicle is running on the expresswayand the vehicular apparatus 100 can no longer receive guidanceinformation for the route ahead, the vehicular apparatus 100 can stillgive guidance for the major guide points and the operator can therebyacquire a minimum amount of guidance.

[0145] In the above example, since the present position is on anexpressway, the vehicular apparatus 100 judges that the vehicle haspassed the entrance interchange of the expressway that is the firstmajor guide point. Accordingly, the vehicular apparatus 100 does notacquire information relating to the entrance interchange and proceeds tojudge whether the vehicle has passed the service area which is thesecond major guide point. If the vehicle has not passed the service areayet, the vehicular apparatus 100 acquires information relating to theservice area and then information for the interchange at which to exitthe expressway as the third major guide point. The vehicular apparatus100 gives guidance for the second and third major guide points. That is,a message to the effect that the vehicle should exit the expressway atthe exit interchange, after passing the service area, is given to theoperator in the form of display on the display section 106 or voiceoutput from the voice output section 107.

[0146] In this manner, the operator can reach the destination utilizingreliable guidance, through a minimum amount of guidance, withoutbecoming confused by improper route guidance.

[0147] The invention is not limited to the above-described embodiment.Various modifications are possible without departing from the spirit andscope of the invention.

[0148] As described above, according to the invention, even whencommunication between the information center and the vehicular apparatusis disabled, proper guidance can be provided in the form of guidance formajor guide points.

[0149] Embodiment 2

[0150] A communication-type car navigation system according to a secondembodiment of the invention will be described with reference to FIGS.9-14.

[0151]FIG. 9 shows the configuration of the communication-type carnavigation system according to the second embodiment. As shown in FIG.9, the communication-type car navigation system includes an informationdelivery center (hereinafter referred to simply as “information center”)1 and a vehicular route guidance apparatus (“vehicular apparatus), i.e.,a navigation apparatus provided in a car.

[0152] The information center 1 is equipped with atransmission/reception section 10, a computation section 20, a database31, and an external information collecting section 40. In the form of acommunication device including a transmitter and a receiver, thetransmission/reception section 10 exchanges data with the vehicularapparatus 2. The transmission/reception section 10 can use a vehiculartelephone, cellular phone, PHS, or like communication system.

[0153] The computation section 20 serves as a search means, atransmitting means, a preliminary route guidance information generatingmeans, and a remaining route guidance information generating means, andis equipped with a central processing unit (CPU) 21 that performscomputations and a memory 22 that stores various programs and data. Thememory 22 contains various programs to be executed in the informationcenter 1, such as a route search program 22 a, a road length settingprogram 22 b, a guidance information extracting program 22 c, apreliminary/remaining route generating program 22 d, and a systemcontrol program 22 e. A working area to be used when any of thoseprograms is executed is provided in the memory 22.

[0154] The route search program 22 a is a program that is executed bythe CPU 21 to search for a route from a vehicle present position (e.g.,a navigation start location or a departure location) to a destination(i.e., a navigation end location).

[0155] The road length setting program 22 b is a program that isexecuted by the CPU 21 to set a range for the guidance information to betransmitted to the vehicle, in response to each request, based on roadlength information that is transmitted from the vehicular apparatus 2.If the end of the range of previously generated route guidanceinformation is located on an expressway, the road length setting program22 b sets, in response to a new request, a route guidance rangecorresponding to a route (preliminary route; much shorter than atransmission road length) to an interchange, a service area, or aparking area as an exit point, as well as a remaining route guidancerange corresponding to a remaining route that is the set(“transmission”) road length minus the road length of the preliminaryroute.

[0156] The guidance information extracting program 22 c is a programthat is executed by the CPU 21 to retrieve and edit route guidanceinformation corresponding to a route guidance range that has been set bythe road length setting program 22 b.

[0157] Assume that the end of the range of the route guidanceinformation which was generated in response to a preceding request andwhich corresponds to the set road length is located on a toll road. Thepreliminary/remaining route generating program 22 d is a program that isexecuted by the CPU 21 to search for a route from that end to theclosest interchange, service area, or parking area, ahead of that end,on the toll road (preliminary route search), to search for a remainingroute whose road length is equal to the set road length minus the roadlength of the preliminary route (remaining route search), and toretrieve and edit guidance information for the preliminary route thusfound (preliminary route guidance information) and guidance informationfor the remaining route thus found (remaining route guidanceinformation). The system control program 22 e is a program that isexecuted by the CPU 21 to control and manage the overall operation.

[0158] The database 31 contains data necessary for a route search androute guidance. The data include route search data 31 a to be used forsearching for a route to a destination, guidance data 31 b as anaccumulation of data for route guidance, destination setting data 31 cin the form of telephone numbers and addresses to be set as adestination and positions corresponding to those telephone numbers andaddresses. The route search data 31 a is road network data includingdata relating to intersections, data relating to roads, and datarelating to nodes. The guidance data 31 b includes, for example, mapdata for intersections and roads, major landmark data, and voiceguidance information.

[0159] The database 31 is connected to the external informationcollecting section 40. The external information collecting section 40updates the data stored in the database 31 as necessary by collecting,using telephone lines or the like, the latest road/traffic informationand communication information such as traffic congestion information,traffic accident information, road construction information,regulation-of-traffic information, information indicating a newlyestablished road or facility, and information as to a change innon-communication areas and communication-defective areas. Each piece oftraffic congestion information, traffic accident information, roadconstruction information, regulation-of-traffic information, andinformation indicating a newly established road or facility is collectedin the form of a location and a date and time of occurrence and otherinformation. For example, for traffic congestion information, a locationand a date and time of occurrence of a traffic jam and other informationare collected. The other types of information such as traffic accidentinformation are collected in similar fashion.

[0160] The vehicular apparatus 2 includes a transmission/receptionsection 51, a position determination section 52, a computation section53 that serves as a route guidance means and a re-search means, a memory54, an input section 55, a display section 56, a voice output section 57in the form of a speaker, and an external storage device 58 which servesas a road data storing means.

[0161] As a communication device including a transmitter and a receiver,the transmission/reception section 51 exchanges data with theinformation center 1. Like the transmission/reception section 10 of theinformation center 1, the transmission/reception section 51 can use avehicular telephone, cellular phone, PHS, or like communication system.The transmission/reception section 51 is also equipped with a receiverfor receiving optical beacon information as route information that istransmitted from beacons which are provided along a road and whichtransmit, to vehicles, traffic congestion information,regulation-of-traffic information, etc., for a limited area in a systemreferred to as a VICS (vehicle information and communication system).

[0162] The position determination section 52 is a section fordetermining a vehicle position using the GPS etc., and is equipped witha GPS receiver for determining the a vehicle absolute position byreceiving signals from a plurality of GPS satellites and with acombination of a speed sensor, a direction sensor, etc., for measuring avehicle relative position. The speed sensor and the direction sensor areused for independent navigation. For example, a relative position thatis determined by these sensors is used as the vehicle position in atunnel or the like where the GPS receiver cannot receive radio signalsfrom the GPS satellites or correct for an error in the absolute positionthat is determined by the GPS receiver.

[0163] The computation section 53, the main part of which is a CPU,performs various types of computations according to various programsstored in the memory 54.

[0164] The memory 54 has a program storage area 54 a that contains aroute guidance program 61, a data request program 62, a control program63, a preliminary route request program 64, a route search program 65, aguidance information extracting program 66, a communication failurecountermeasure program 67, etc. The route guidance program 61 is aprogram that is executed by the computation section 53 for display of aroute and landmarks based on route guidance information that istransmitted from the information center 1 and for output of a routeguidance voice from the voice output section 57. The data requestprogram 62 is a program that is executed by the computation section 53for comparing a vehicle present position with the received routeguidance information and for requesting further route guidanceinformation. The control program 63 is a program that is executed by thecomputation section 53 to control the overall operation of the vehicularapparatus 2.

[0165] The preliminary route request program 64 is a program that isexecuted by the computation section 53 for comparing a vehicle presentposition with the received route guidance information and for requestingroute guidance information (preliminary route guidance information) fora route (preliminary route) to the next interchange, service area, orparking area.

[0166] The route search program 65 is a program that is executed by thecomputation section 53 to search for a route to a destination using theroad network data for a route search which is stored in the externalstorage device 58 and which includes data relating to intersections,data relating to roads, and data relating to nodes when route guidanceinformation (including preliminary route guidance information) cannot bereceived from the information center 1 by the communication failurecountermeasure program 67.

[0167] The guidance information extracting program 66 is a program thatis executed by the computation section 53 to retrieve and edit a routethat has been found by the route search program 65.

[0168] The communication failure countermeasure program 67 is a programthat is executed by the computation section 53 to perform various typesof route guidance when communication with the information center 1 hasbeen interrupted and route guidance cannot be performed using routeguidance information transmitted from the information center 1.

[0169] The memory 54 also has a data storage area 54 b as a routeguidance information storing means. The data storage area 54 b functionsas a working area that is used as necessary in executing any of theabove-mentioned various programs, and contains route guidance data 71which includes route guidance information transmitted from theinformation center 1, ID data 72 that is unique to the associatedvehicle, vehicle position data 73 that is obtained by the positiondetermination means 52, and other data.

[0170] The route guidance data 71 includes, in addition to routeguidance information, preliminary route guidance information that isalso transmitted from the information center 1. The vehicle positiondata 73 includes, in addition to present position information that isrepeatedly obtained by the position determination section 52 at apredetermined time interval, items of past position information. Forexample, the vehicle position data 73 includes items of positioninformation for measurement points at predetermined distances or itemsof position information for a predetermined number of measurementpoints. When a new determination has been made by the positiondetermination section 52, the thus obtained most recent positioninformation is stored and the oldest position information is erased. Avehicle running locus can be obtained by connecting those items ofposition information. The vehicle running locus is used for map matchingfor determining the road on which the vehicle is currently travelling.

[0171] The input section 55 includes various switches, a touch panelthat is attached to the display screen of the display section 56, aremote controller, a speech recognition data input device, etc. When theuser touches the touch panel at an icon or the like that is displayed onthe display section 56, a corresponding instruction or item ofinformation is input. The speech recognition data input devicerecognizes the voice of the user, whereby a corresponding instruction oritem of information is input.

[0172] The display section 56 is a liquid crystal display, a CRTdisplay, or the like and is equipped with the above-mentioned touchpanel.

[0173] The external storage device 58 has a storage medium such as a DVDor a CD-ROM on which data relating to maps, data relating to roads,etc., is recorded. The data relating to maps, the data relating toroads, etc., that is recorded on the recording medium is used when thevehicular apparatus 2 itself searches for a route to a destination andgenerates route guidance information, because it cannot receive routeguidance data from the information center 1. The external storage device58 may be a device having a writable recording medium, such as a harddisk drive. In this case, the user may acquire data relating to maps anddata relating to roads from the information center 1 (e.g., an Internetserver) and record that data on the recording medium.

[0174] Next, the operations of the information center 1 and thevehicular apparatus 2 having the above-described configurations will beexplained.

[0175] Operation of the Information Center

[0176] First, the operation of the information center 1 will bedescribed with reference to the flowchart of FIG. 10, which shows aroute search/guidance information transmission operation of theinformation center 1.

[0177] In the vehicular apparatus 2, the control program 63 that isstored in the memory 54 is executed by the computation section 53. Inthis state, if the data request program 62 that is stored in the memory54 is executed in response to an input by the user, various types ofinformation, that is, the vehicle present position that has beendetermined by the position determination section 52, direction oftravel, the destination, the type of road on which the vehicle presentposition is located, the search condition, if any, (e.g., priority givento toll roads or ordinary roads), and the set road length (a road lengthset for transmission) indicating a range for which route guidance isneeded, are transmitted from the transmission/reception section 51 tothe information center 1. The ID of the associated vehicle istransmitted at the same time to differentiate the associated vehiclefrom other vehicles.

[0178] In the information center 1, the above items of information arereceived by the transmission/reception section 10 (“yes” at step S111)and supplied to the computation section 20. Packet communication isperformed between the information center 1 and the vehicular apparatus2.

[0179] The computation section 20 of the information center 1 executesthe system control program 22 e that is stored in the memory 22.Receiving the items of information from the vehicular apparatus 2, theCPU 21 performs a route search by executing the route search program 22a that is stored in the memory 22. First, the CPU 21 extracts, from thereceived information, items of information such as the vehicle presentposition information, the destination information, the travel direction,the type of road on which the present position is located, the searchcondition, and the set transmission road length (step S112), andsearches for a route from the vehicle present position to thedestination based on the extracted items of information (step S113).

[0180] The route search is performed by referring to the route searchdata 31 a of the database 31, that is, the intersection data, the roaddata, and the node data. The route search operation itself is a knowntechnique. A recommended route is set under prescribed conditions suchas a condition that the route whose overall length is the shortestshould be designated as the optimum route (refer to Japanese PatentLaid-Open Nos. 173297/1989 and 173298/1989).

[0181] Then, the CPU 21 of the computation section 20 of the informationcenter 1 executes the guidance information extracting program 22 c thatis stored in the memory 22 and thereby retrieves, by referring to theguidance data 31 b of the database 31, information of a range that wasset by the road length setting program 22 b (step S114). The extractedroute guidance information is stored temporarily in the memory 22 asroute guidance data 22 f. The CPU 21 of the computation section 20causes the transmission/reception section 10 to transmit the routeguidance data 22 f to the vehicular apparatus 2 together with the ID ofthe vehicle that made the request (step S115).

[0182] If the end of the route section, for which route guidanceinformation has been previously generated and transmitted, is located onan expressway, the road length setting program 22 b sets a routeguidance range corresponding to a route (preliminary route; much shorterthan a transmission road length) from the end of that section located onan expressway to the closest interchange, service area, or parking areaahead. The CPU 21 executes the guidance information extracting program22 c and thereby retrieves, by referring to the guidance data 31 b ofthe database 31, guidance information for the route guidance range thusset (step S114). The extracted route guidance information (preliminaryroute guidance information) is stored temporarily in the memory 22 asroute guidance data 22 f. The CPU 21 of the computation section 20causes the transmission/reception section 10 to transmit the routeguidance data 22 f to the vehicular apparatus 2 together with the ID ofthe vehicle that made the request (step S115).

[0183] Then, the road length setting program 22 b sets a remaining routeguidance range for the remaining route which is equal to the settransmission road length minus the road length of the preliminary route.The CPU 21 then executes the guidance information extracting program 22c and thereby retrieves, by referring to the guidance data 31 b of thedatabase 31, guidance information for the remaining route guidance rangethus set (step S114). The extracted route guidance information(remaining route guidance information) is stored temporarily in thememory 22 as route guidance data 22 f. The CPU 21 of the computationsection 20 causes the transmission/reception section 10 to transmit theroute guidance data 22 f to the vehicular apparatus 2 together with theID of the vehicle that made the request (step S115).

[0184] The transmission of the preliminary route guidance information(route guidance data 22 f) of the preliminary route is completed in ashort time because the preliminary route is relatively short and hencethe amount of data is small. In contrast, the transmission of theremaining route guidance information (route guidance data 22 f) for theremaining route, i.e., the recommended route minus the preliminaryroute, takes a much longer time than the transmission of the preliminaryroute guidance information because the remaining route is longer thanthe preliminary route and hence the amount of data is larger.

[0185] In this embodiment, the information center 1 searches for a routefrom a vehicle present position to the destination every time itreceives a request from the vehicular apparatus 2. In the informationcenter 1, the external information collecting section 40 acquires roadinformation, traffic information, etc. from the external sources and thedatabase 31 is updated accordingly. By virtue of a route searchperformed in response to each request from the vehicular apparatus 2,the information center 1 can supply the vehicular apparatus 2 with arecommended route that has been determined based on the latest data insuch a manner as to avoid traffic jams, construction locations, accidentlocations, and the like, or to use a new road, as well as guidanceinformation for the recommended route.

[0186] Operation of the Vehicular Apparatus

[0187] Next, the operation of the vehicular apparatus 2 will bedescribed with reference to flowcharts of FIGS. 11 and 12, which show arequesting and route guidance routine executed by the vehicularapparatus 2.

[0188] At step S131, the user sets a destination by using prescribedswitches of the input section 55. At step S132, the user sets a searchcondition (giving priority to an ordinary road or to a toll road). Forconvenience of description, it is assumed that the search condition thatpriority is given to a toll road or expressway has been set. When thedestination and the search condition have been set, at step S133 thecomputation section 53 of the vehicular apparatus 2 judges whether toacquire route guidance information for a route to the destination usingthe information center 1 or using the route search program 65 of thevehicular apparatus 2 itself. This judgment is performed based on asetting that has been made in advance by using a prescribed switch ofthe input section 55. In this embodiment, for convenience ofdescription, it is assumed that a selection has been made that routeguidance data of a route to the destination should be acquired by usingthe information center 1.

[0189] Therefore, judging that route guidance information should beacquired from the information center 1 (“yes” at step S133), thecomputation section 53 of the vehicular apparatus 2 goes to step S134,where it transmits, to the information center 1, together with an ID,information identifying the destination, the search condition, a vehiclepresent position that has been determined by the position determinationsection 52, and a road length, as necessary for a route search andextraction of guidance information. Then, the computation section 53receives, from the information center 1, the results of the route searchthat has been performed by the information center 1 based on theinformation as to the destination, the vehicle present position, thesearch condition, the transmission road length, etc. More specifically,the information center 1 transmits the search results for a rangecorresponding to the set transmission road length. The computationsection 53 receives it and stores it temporarily in the data storagearea 54 b of the memory 54 (step S135), and then performs a guidanceinformation receiving operation (step S136).

[0190]FIG. 13 is a flowchart showing a guidance information receivingsubroutine. Referring to FIG. 13, if the end of a section of therecommended route, for which route guidance information has beenpreviously received, lies on an expressway, the computation section 53requests the information center 1 to send back position information foran interchange (IC), a service area (SA), or a parking area (PA) (stepS161; “no” at step S162) and receives, from the information center 1,route guidance information (preliminary route guidance information) fora route to an interchange, a service area, or a parking area. Then, thecomputation section 53 judges whether all the preliminary route guidanceinformation for the route to the interchange, service area, or parkingarea has been received. If it has been received completely (“yes” atstep S164), the computation section 53 requests the information center 1to send back remaining route guidance information for the remainingroute which is the recommended route minus the preliminary route (stepS166). If the preliminary route guidance information has not beenreceived completely (“no” at step S164), the computation section 53judges that this is due to an interruption of the communication anddisplays an alarm message to that effect on the display section 56.(step S165).

[0191] In response to the request transmitted at step S166, since thisis the first execution of the process and no previous route guidanceinformation has been acquired, route guidance information for a rangecorresponding to the set transmission road length is immediatelytransmitted from the information center 1. The computation section 53 ofthe vehicular apparatus 2 receives this route guidance information andstores it in the data storage area 54 b (step S167). Then, thecomputation section 53 of the vehicular apparatus 2 judges whether allthe route guidance information has been received, that is, whether theroute guidance information has been stored without any break in thecommunication with the information center 1 (step S168). If all theroute guidance information has been stored in the data storage area 54 b(“yes” at step S168), the guidance information receiving operation isfinished and processing returns to the main routine.

[0192] If not all of the route guidance information of the rangecorresponding to the set transmission road length has been stored in thedata storage area 54 b due to a break in the communication (“no” at stepS168), an alarm message to that effect is displayed on the displaysection 56. Then, if preliminary route guidance information was storedinto the data storage area 54 b at step S163, the computation section 53of the vehicular apparatus 2 judges that it is necessary to generate aroute guidance display based on the preliminary route guidanceinformation (step S170). Then, the guidance information receivingoperation is finished and processing returns to the main routine.

[0193] On the other hand, if the end of the route section covered by thepreviously received route guidance information is not on an expressway,the computation section 53 does not request the information center 1 tosend back information on position of an interchange (IC), a service area(SA), or a parking area (PA) (step S161; “yes” at steps S162 and S164)and, instead, requests the information center 1 to send back routeguidance information for a range corresponding to the set transmissionroad length (step S166). Since this is the first execution of theprocess and no previous route guidance information has been acquired,the computation section 53 immediately requests the information center 1to send back route guidance information for a range corresponding to theset transmission road length.

[0194] The computation section 53 of the vehicular apparatus 2 receives,from the information center 1, route guidance information for a rangecorresponding to the set transmission road length and stores it in thedata storage area 54 b (step S167). Then, the computation section 53 ofthe vehicular apparatus 2 judges whether all the route guidanceinformation has been received, that is, whether the route guidanceinformation has been stored without a break in communication with theinformation center 1 (step S168). If all the route guidance informationhas been stored in the data storage area 54 b (“yes” at step S168), theguidance information receiving operation is finished and processingreturns to the main routine.

[0195] Upon return to the main routine and, for example, the car startsrunning or a guidance start switch of the input section 55 is activated,the computation section 53 of the vehicular apparatus 2 starts routeguidance display based on the route guidance data 71 stored in the datastorage area 54 b of the memory 54 (step S140). Route guidance by thevehicular apparatus 2 is started at this point in time.

[0196] If it is judged at step S133 that the vehicular apparatus 2itself should acquire route guidance information for a route to thedestination using its own route search program 65 (“no” at step S133),the computation section 53 starts executing the route search program 65(step S137). The computation section 53 searches for a route to thedestination using the information that is stored in the external storagedevice 58 and acquires a search result (step S138). The computationsection 53 generates route guidance information for a rangecorresponding to the prescribed (e.g., “set”) road length by executingthe guidance information extracting program 66, and stores it in thedata storage area 54 b (step S139). In this case, neither preliminaryroute guidance information nor remaining route guidance information fora range corresponding to the remaining route is generated.

[0197] Then, as in the case where route searches are performed by theinformation center 1, when the car starts to move or the guidance startswitch of the input section 55 is activated, the computation section 53of the vehicular apparatus 2 starts route guidance display based on theroute guidance information that is stored in the data storage area 54 bof the memory 54 (step S140).

[0198] After the route guidance has been started, the computationsection 53 updates the present position on the picture of the displaysection 56 using the route guidance information (step S141). Then, thecomputation section 53 judges whether to update the route guidanceinformation (step S142). As the guidance display is performed based onthe route guidance information for the range corresponding to the settransmission road length that has been received from the informationcenter 1, the route on which the present position is displayed comes totermination point and the route ahead is not displayed. It is thereforenecessary to always secure a predetermined amount of route guidanceinformation. In view of this, in this embodiment, it is judged whetherthe present position has reached a position a prescribed distance fromthe end of the route segment for which route guidance information hasbeen previously received. If the present position has reached such aposition (“yes” at step S142), a guidance information updating operationfor updating the route guidance information, that is, acquiring newroute guidance information for the route ahead, is performed (stepS143). An alternative operation is possible in which a judgement is madeas to whether the vehicle has covered a predetermined distance and aguidance information updating operation is performed (step S143) if thevehicle has covered the predetermined distance (“yes” at step S142).

[0199] The guidance information updating operation is the same as stepsS133-S139 that are enclosed by the broken line in the main routine ofFIG. 11. That is, in the guidance information updating operation, toacquire route guidance information to the destination from theinformation center 1, route guidance information for a rangecorresponding to the next set transmission road length (recommendedroute segment length) or preliminary route guidance information andremaining route guidance information for a range corresponding to aroute segment minus the preliminary route.

[0200] Thus, in the guidance information updating operation, if the endof the route section covered by the preceding route guidance informationis on an expressway, preliminary route guidance information is firstreceived and then remaining route guidance information for a rangecorresponding to a route segment of set length minus the preliminaryroute is received.

[0201] When the route guidance has just started, the vehicle has notreached a position the prescribed distance from the end of a routesegment for which guidance data has been received. Therefore, thecomputation section 53 searches the current route guidance information(route guidance data 71) for information to be provided as guidance(step S144). If information to be provided as guidance is found in thecurrent route guidance information (route guidance data 71) (“yes” atstep S145), the computation section 53 outputs the information to beprovided as guidance to the display section 56 (step S146).

[0202] Conversely, if no information to be provided as guidance is foundin the current route guidance information (“no” at step S145), thecomputation section 53 judges whether the communication with theinformation center 1 has been interrupted due to an abnormalcommunication state (step S147). If no abnormal communication stateexists (“no” at step S147), the computation section 53 recognizes thatthere is no information to be provided as guidance (step S146).

[0203] Then, the computation section 53 judges whether the vehicle hasreached the destination or a guidance stop switch of the input section55 has been activated (step S148). If the vehicle has not yet reachedthe destination and the guidance stop switch of the input section 55 hasnot been activated (“no” at step S148), the process returns to stepS141. Conversely, if the vehicle has reached the destination or theguidance stop switch of the input section 55 has been activated (“yes”at step S148), the computation section 53 finishes the route guidance.

[0204] From this time forward, so long as the communication is notdisrupted (“broken” or “lost”), route guidance is performed untilreaching the destination while the route guidance information is updatedin the guidance information updating operation of step S143, that is,new route guidance information for the route ahead is received andstored as route guidance data 71, each time the vehicle has covered thepredetermined distance (“set transmission road length” or “prescribedlength”). When the vehicular apparatus 2 has received new route guidanceinformation, if the end of the route segment covered by the most recentprevious route guidance information is on an expressway (or a toll road)and the expressway (or the toll road) extends along the recommendedroute from that segment end, the vehicular apparatus 2 receivespreliminary route guidance information and stores it also as routeguidance data 71 and then receives remaining route guidance informationand stores it as route guidance data 71.

[0205] On the other hand, if an abnormal communication state hasoccurred (“yes” at step S147), the computation section 53 judges whetherit is necessary to give guidance based on the route guidance data 71stored in the data storage area 54 b of the memory 54 (step S149). Ifroute guidance for the present position can be given satisfactorilybased on primary route guidance information (i.e., route guidanceinformation for a range corresponding to the set transmission roadlength or route guidance information for a range corresponding to aremaining route, i.e., the route corresponding to the set transmissionroad length minus a preliminary route, (“no” at step S149), an alarmmessage to the effect that the communication has been interrupted isdisplayed on the display section 56 (step S151) and the process goes tostep S148.

[0206] Therefore, even if an abnormal communication state has occurred,when route guidance for the present position is being given based ononly primary route guidance information, the vehicular apparatus 2performs route guidance based on the primary route guidance informationwhile displaying a message to the effect that an abnormal communicationstate has occurred.

[0207] If it is judged that guidance for the present position needs tobe given based on the preliminary route guidance information (“yes” atstep S149), a preliminary route guidance operation is performed in whichguidance is given until the vehicle reaches the interchange, servicearea, or parking area by using the preliminary route guidanceinformation (route guidance data 71) that is stored in the data storagearea 54 b of the memory 54 (step S150).

[0208] If the communication with the information center 1 is interruptedduring a lengthy transmission, from the information center 1, of routeguidance information of a range corresponding to a set transmission roadlength, all the route guidance information of that transmission(including that part which has already been received) is lost and hencethe route ahead of the end of the route segment covered by the guidancedisplay, based on the route guidance information that is stored in thedata storage area 54 b of the memory 54, will not be displayed.Accordingly, if the end of the route segment covered by the precedingroute guidance information is on an expressway, preliminary routeguidance information which can be transmitted in a short time is firsttransmitted and then the remaining route guidance information for theremainder of the route segment, that is the route segment which is thesubject of the current transmission minus the preliminary route, whichtransmission takes a significantly longer time, is then transmitted.That is, the new route guidance information is transmitted in two partpackets, the first packet part being the first route guidance data 71(preliminary route guidance information) transmitted, which data can betransmitted within a short period of time to guard against thepossibility that communication might be lost during travel of that routesegment which is the subject of the current transmission. In thismanner, at least the preliminary route guidance information is reliablyreceived.

[0209] If it is judged that guidance needs to be given for the presentposition based on the first-received preliminary route guidanceinformation, in the case where the first-received preliminary routeguidance information has been received and stored (“yes” at step S149),a preliminary route guidance operation is performed using thepreliminary route guidance information (route guidance data 71) (stepS150).

[0210]FIG. 14 is a flowchart showing a preliminary route guidancesubroutine. Referring to FIG. 14, the computation section 53 acquirespresent position information from the position determination section 52(step S181) and extracts information data for an interchange, a servicearea, or a parking area (step S182). Then, the computation section 53compares the present position with the position of the interchange,service area, or parking area and judges whether the present positionhas passed (reached) the position of the interchange, service area, orparking area (step S183).

[0211] If the present position has not yet reached the position of theinterchange, service area, or parking area (“no” at step S183), thecomputation section 53 gives route guidance using the preliminary routeguidance information and the process goes to step S151 of the mainroutine. In this manner, even when part of an expressway (or a tollroad) ahead can not be displayed while the vehicle is running on theexpressway, route guidance can be performed until the vehicle reachesthe nearest interchange, service area, or parking area ahead.

[0212] Conventionally, where data for a new expressway (or toll road) isnot stored in the external storage device 58 of the vehicular apparatus2, improper route guidance is given in that the vehicle present positionis displayed without showing the new expressway. In contrast, even ifthe communication has been disrupted so that no route guidanceinformation can be acquired from the information center 1, guidance fora route (preliminary route) to an interchange of the new expressway,where it connects to a road for which data is stored in the externalstorage device 58 of the vehicular apparatus 2, allows the vehicle totravel without guidance to the position from which route guidance can beperformed.

[0213] When the present position has reached the interchange, servicearea, or parking area (“no” at step S183), the computation section 53judges that the vehicle has reached the closest interchange, servicearea, or parking area and initializes the preliminary route guidanceinformation (step S184). The route guidance using the preliminary routeguidance information is thus finished and the process goes to step S151of the main routine.

[0214] If the vehicle reaches the interchange, for example, andcommunication with the information center 1 remains impossible andremaining route guidance information for a remaining route segment aheadof the preliminary route has not yet been received, the vehicularapparatus 2 performs route guidance from the interchange to thedestination by executing its own route search program 65 and guidanceinformation extracting program 66 using the information stored in theexternal storage device 58. After reaching the service area or theparking area, the vehicle may stay there waiting for recovery ofcommunication with the information center 1.

[0215] Next, advantages of the above communication-type car navigationsystem will be described.

[0216] (1) In this embodiment, if the end of a route segment covered bythe preceding route guidance information is on an expressway,preliminary route guidance information which can be transmitted in ashort time is transmitted first and then remaining route guidanceinformation for the remaining route segment (a route segment minus thepreliminary route), the transmission of which takes a longer time, istransmitted. That is, new route guidance information is transmitted intwo transmission parts, with the preliminary route guidance informationtransmitted first, within a relatively short time, to guard against thepossibility that communication might be lost during travel of the routesegment covered by the current transmission. In this manner, thevehicular apparatus 2 can receive the preliminary route guidanceinformation so quickly that the probability of disconnection ofcommunication during transmission of same is low.

[0217] (2) In this embodiment, new route guidance information for eachsuccessive route segment is transmitted as two transmissions with thepreliminary route guidance information is transmitted first within ashort time. Even if lack of communication with the information center 1persists and guidance for part of an expressway (or a toll road) aheadof the present position can not be displayed, preliminary route guidancecan be provided for guidance to an interchange, a service area, or aparking area that is ahead of and closest to the present position, i.e.,a route (preliminary route) can be displayed until the vehicle reachesan interchange, a service area, or a parking area that is ahead of andclosest to the present position. This can prevent improper routeguidance wherein the vehicle present position is displayed on the screenbut part of a new expressway (or toll road) ahead of the presentposition can not be displayed because data for the new expressway (ortoll road) is not stored in the external storage device 58 of thevehicular apparatus 2.

[0218] (3) Further, in this embodiment, once guidance is given for apreliminary route to an interchange, the vehicular apparatus 2 canproperly perform route guidance from the interchange to a destinationusing ordinary roads by executing the route search program 65 and theguidance information extracting program 66 that are stored in theexternal storage device 58, even if a communication failure disablesroute guidance using route guidance information that should betransmitted from the information center 1, because the interchange isconnected to an ordinary road for which data is stored in the externalstorage device 58 of the vehicular apparatus 2.

[0219] (4) In this embodiment, where a service area or a parking areaexists before an interchange, guidance is given for a preliminary routeto the service area or the parking area. In this case, the vehicle canstay in the service area or the parking area waiting for recovery ofcommunication with the information center 1.

[0220] This embodiment may be modified in the following manners:

[0221] In the embodiment, preliminary route guidance informationcorresponding to one of an interchange, a service area, and a parkingarea, that is closest to the end of the route segment covered by thepreceding route guidance information, is generated. Alternatively,preliminary route guidance information corresponding to the interchange,rather than the service area or the parking area, that is closest to theend of the route segment covered by the preceding route guidanceinformation may be generated. Conversely, preliminary route guidanceinformation corresponding to the service area or the parking area,rather than the interchange, that is closest to the end of the routesegment covered by the preceding route guidance information may begenerated.

[0222] As a further alternative, both the preliminary route guidanceinformation corresponding to the interchange that is closest to the endof the route covered by the preceding route guidance information andthat corresponding to the service area or the parking area that isclosest to the end of the route segment covered by of the precedingroute guidance information may be generated.

[0223] In the embodiment described above, a transmission correspondingto a set road length is transmitted from the vehicular apparatus 2 tothe information center 1 and the information center 1 generates routeguidance information to be transmitted in one attempt (attempted oreffected transmission) based on the transmission road length.Alternatively, the information center 1 determines a road length andgenerates route guidance information to be transmitted to the vehicularapparatus 2 in one attempt based on the determined road length.

[0224] In the described embodiment, when a state of abnormalcommunication has arisen, route guidance is automatically performed byusing preliminary route guidance information. Alternatively, whether toperform route guidance using preliminary route guidance information maybe determined by the user by activation a switch of the input section55.

[0225] In the described embodiment, the exit (“escape”) location is aninterchange, a service area, or a parking area of an expressway (or atoll road). In the case of a multi-level toll road, the exit locationmay be an upper level of the multi-level toll road. In this case, theroad search data 31 a should include upper level information for themulti-level road.

[0226] According to the present invention, when the communicationbetween the information delivery center and the vehicular route guidanceapparatus is disrupted and guidance for part of a toll road (orexpressway) ahead of its position can not be displayed, preliminaryroute guidance is given from that position to an escape position aheadusing preliminary route guidance information. This can prevent improperroute guidance where the vehicle present position would be displayed onthe screen without display of that part of a new toll road (orexpressway) ahead of its present position, i.e., where the data for thenew toll road (or expressway) is not stored in the road data storingmeans of the vehicular route guidance apparatus.

[0227] According to the invention, since an escape position(interchange, service area, or parking area) on the toll road (orexpressway) is ahead of and closest to the above-mentioned presentposition, the vehicle can reach the escape position in a short time andcan wait there for restoration of communication.

[0228] Embodiment 3

[0229] Next, modifications (third embodiment) of the above informationcenter 1 and vehicular apparatus 2 will be described.

[0230] In this third embodiment, the information center 1 searches for aroute from a vehicle present position to a destination every time itreceives a request from the vehicular apparatus 2. In the informationcenter 1, the external information collecting section 40 acquires roadinformation, traffic information, etc. from external sources and thedatabase 31 is updated accordingly. By virtue of the procedure that aroute search is performed in response to each request from the vehicularapparatus 2, the information center 1 can supply the vehicular apparatus2 with a recommended route that has been determined based on the latestdata and in such a manner as to avoid traffic jams, constructionlocations, traffic accidents, and the like or to use a new road, as wellas guidance information for the recommended route.

[0231] Next, the operation of the vehicular apparatus 2 will bedescribed with reference to FIG. 15 which illustrates the operation ofacquiring route guidance information from the information center 1 andcausing the display section 56 and the voice output section 57 of thevehicular apparatus 2 to output route guidance information for a routeto a destination for each transmission.

[0232] At step S221, the computation section 53 of the vehicularapparatus 2 transmits, to the information center 1, together with an ID,information as to the vehicle present position that has been determinedby the position determination section 52, direction of travel, type ofroad on which the present position is located, destination, transmissionroad length, and a search condition. Then, the computation section 53waits for reception of route guidance information to be transmitted fromthe information center 1 in response to receipt of the above information(step S222).

[0233] When receiving route guidance information that is transmittedfrom the information center 1 (“yes” at step S222), the computationsection 53 stores the received route guidance information in the datastorage area 54 b of the memory 54 as route guidance data 71. Then, thecomputation section 53 generates guidance using the received routeguidance information (route guidance data 71) by executing the routeguidance program 61 (step S223). That is, a map including a route andlandmarks is displayed on the display section 56 and a guidance voice isoutput from the voice output section 57 when, for example, a right orleft turn is necessary at an intersection.

[0234] At the same time, the computation section 53 refers to a vehiclepresent position in the position measuring section 52 and executes thedata request program 62. If the vehicle present position has reached aposition a predetermined distance (e.g., 200 m) from the end of thereceived route segment, the computation section 53 requests the nextpacket of route guidance information (“yes” at step S224). In response,the same operations as were performed above in response to theinformation that was transmitted to the information center 1 at stepS221 are performed in the information center 1 and the resulting packetof new route guidance information is transmitted to the vehicularapparatus 2.

[0235] On the other hand, if the next route guidance information packetis not requested (“no” at step S224), the computation section 53 judgeswhether all route guidance information necessary for guidance to reachthe destination has been received (step S225). The operation is finishedif all route guidance information has been received.

[0236] In summary, the vehicular apparatus 2 transmits, to theinformation center 1, information of a vehicle present position, traveldirection, type of road on which the present position is located, adestination, a transmission road segment length, and a search condition.The information center 1 performs a route search based on the receivedinformation and generates route guidance information (route guidancedata 22 f). The information center 1 transmits the generated routeguidance information to the vehicular apparatus 2 and the vehicularapparatus 2 performs route guidance based on the received route guidanceinformation (route guidance data 71).

[0237] Route guidance information (route guidance data 71) that is nolonger necessary is discarded. When continuation route guidanceinformation has become necessary (step S224), the vehicular apparatus 2again transmits, to the information center 1, information of a vehiclepresent position, travel direction, type of road on which the presentposition is located, destination, transmission road segment length, anda search condition (step S221). Similar operations are thereafterrepeated until the vehicle reaches the destination.

[0238] Next will be described an operation that is performed by thevehicular apparatus 2 when a failure has occurred in the communicationwith the information center 1, which failure prevents acquisition ofroute guidance information from the information center 1. Thisembodiment is characterized in how to deal with the situation whicharises when a failure in communication prevents acquisition of routeguidance information for a route segment ahead of the present position,as described below in detail.

[0239]FIG. 16 is a flowchart showing an operation that is performed bythe computation section 53 of the vehicular apparatus 2 by execution ofcommunication failure countermeasure program 67 when route guidanceinformation for the route segment ahead of the present position is notavailable due to a failure in communication. For convenience ofdescription, it is assumed that an abnormal communication state hasarisen during the vehicle's travel on an expressway (or a toll road)which prevents acquisition of route guidance information for a routesegment ahead of the present position.

[0240] First, the computation section 53 judges whether communicationwith the information center 1 has recovered (step S241). Ifcommunication has not yet recovered (“no” at step S241), the computationsection 53 judges whether optical beacon information has been received(step S242). In general, VICS optical beacons are installed alongsideordinary roads. The receipt of optical beacon information by thetransmission/reception section 51 means that the vehicle has enteredonto ordinary road upon exit from the expressway. Therefore, whenreceiving optical beacon information via the transmission/receptionsection 51, the computation section 53 judges that the vehicle exitedthe expressway and is now travelling on an ordinary road.

[0241] If no optical beacon information has been received (“no” at stepS242), that is, if the computation section 53 judges that the vehicle isnot travelling on an ordinary road that is provided with VICS opticalbeacons, the computation section 53 judges whether a re-search switch ofthe input section 55 has been activated to cause the vehicular apparatus2 to perform a re-search (step S243). That is, the computation section53 judges whether the user has recognized an abnormal communicationstate and has performed a manual action to cause the vehicular apparatus2 to search for a route to the destination using the data of theexternal storage device 58, by execution of the route search program 65.

[0242] If the re-search switch of the input section 55 has not beenactivated (“no” at step S243), the computation section 53 judges whetherthe vehicle has passed an interchange for exit from the expressway ontoan ordinary road (step S244). Specifically, the computation section 53calculates curvature of each road section of a predetermined length onwhich the vehicle is travelling and judges whether the calculatedcurvature, which represents a road shape, coincides with curvature of alooped interchange that is stored in the memory 54 in advance. If thecalculated road curvature coincides with curvature of a loopedinterchange, the computation section 53 judges that the vehicle hasexited the expressway at that interchange to enter onto an ordinaryroad. Conversely, if the calculated road curvature does not coincidewith curvature of any looped interchange, the computation section 53judges that the vehicle has not exited the expressway at an interchange.

[0243] If the computation section 53 judges that the vehicle has notexited the expressway at an interchange (“no” at step S244), thecomputation section 53 prohibits map matching (step S245). That is, thecomputation section 53 prohibits map matching with a judgment that thevehicle continues to run on the expressway after the occurrence of thecommunication failure and the re-search switch of the input section 55has not been activated. Since map matching has been prohibited, theprocess goes to step S241 without again searching for a route to thedestination by the computation section 53. At step S241, the computationsection 53 again judges whether communication with the informationcenter 1 has recovered.

[0244] As described above, the computation section 53 of the vehicularapparatus 2 does not perform map matching or a re-search if acommunication failure occurred while the vehicle was running on anexpressway and the vehicle is still running on the expressway with thecommunication failure continuing. As a result, for example, in the casewhere the expressway is a new expressway and the road data for the newexpressway is not stored in the external storage device 58 of thevehicular apparatus 2, the vehicular apparatus 2 does not provide animproper display or improper route guidance, i.e., guidance by which thevehicle present position would be erroneously shown on the closestordinary road for which road data is stored in the external storagedevice 58, rather than correctly shown on the new expressway by mapmatching.

[0245] If communication with the information center 1 recovers while thevehicle is travelling in the state that map matching and a routere-search are prohibited (“yes” at step S241), the computation section53 requests the information center 1 to perform a route search (stepS246) and transmits, to the information center 1, information for thevehicle present position, travel direction, type of road on which thepresent position is located, destination, transmission road segmentlength, and search condition (step S247).

[0246] The vehicular apparatus 2 receives route guidance informationgenerated by the information center 1 in due course (step S248) and thecomputation section 53 performs map matching based on the received routeguidance information (route guidance data 71) (step S249). From thistime forward, the vehicular apparatus 2 performs route guidance based onthe route guidance information received (route guidance data 71) incommunication with the information center 1.

[0247] On the other hand, if optical beacon information has beenreceived (“yes” at step S242), the computation section 53 judges thatthe vehicle is running on an ordinary road and judges whether thevehicle was running on the expressway when the communication failureoccurred (step S250). If the vehicle was running on an expressway whenthe communication failure occurred (“yes” at step S250), the computationsection 53 performs map matching with a judgment that the ordinary roadthat the vehicle entered after exiting the expressway is an ordinaryroad for which road data is stored in the external storage device 58(step S251). That is, the vehicular apparatus 2 performs map matchingwith a judgment that the road data of its own external storage device 58has become usable.

[0248] If the vehicle present position has been determined to be off theexpressway as a result of the map matching (“yes” at step S252), thecomputation section 53 searches for a route from the present position tothe destination according to the route search program 65 (step S253).From this time forward, the vehicular apparatus 2 provides routeguidance by executing the route guidance program 61 using the road dataof the external storage device 58 until communication with theinformation center 1 is restored. Conversely, if the road on which thevehicle present position is located cannot be identified by map matching(“no” at step S252), the computation section 53 finishes execution ofthe routine without performing a route search. That is, the computationsection 53 judges that the ordinary road which the vehicle entered afterexiting the expressway is an ordinary road for which road data is notstored in the external storage device 58, in recognition of the factthat a route search with forcible map matching using the road data ofthe external storage device 58 will lead to improper route guidance.

[0249] If it is judged that the vehicle has exited the expressway at aninterchange to enter an ordinary road (“yes” at step S244), thecomputation section 53 judges that the vehicle is now travelling on anordinary road and performs map matching (step S251). That is, thecomputation section 53 performs map matching with a judgment that thevehicle is running on an ordinary road for which road data is stored inthe external storage device 58 and a route search using the road data ofthe external storage device 58 has become possible. From this timeforward, the computation section 53 executes steps S252 and S253 as inthe above-described case and finishes the execution of the program.

[0250] If the re-search switch of the input section 55 has beenactivated (“yes” at step S243), the computation section 53 performs mapmatching using the road data of the external storage device 58 accordingto the user's intention (step S251). The computation section 53 thenexecutes steps S252 and S253 as in the above-described case and finishesthe execution of the program.

[0251] If it is judged that the vehicle was not running on theexpressway when a communication failure occurred (“no” at step S250),the process goes to step S245. The process then returns to step S241.That is, in the case where when the communication failure occurred whilethe vehicle was running on a road other than an expressway (or a tollroad), such as a new bypass that is provided with optical beacons, andits road data is not stored in the external storage device 58 of thevehicular apparatus 2, the vehicular apparatus 2 does not performimproper display and route guidance with the vehicle present positionindicated to be on an ordinary road for which road data is stored in theexternal storage device 58, rather than on the new bypass.

[0252] Next, advantages of the above communication-type vehiclenavigation system will be described below.

[0253] (1) In this third embodiment, if the communication with theinformation center 1 is disrupted (lost) while the vehicle is running onan expressway (or a toll road) and there remains no route portion thatis associated with route guidance information, the computation section53 prohibits map matching and a route search using the road data of theexternal storage section 58 as long as the vehicle continues to run onthe expressway (“no” at steps S242 and S244).

[0254] Therefore, in the case where the expressway where thecommunication failure occurred is a new expressway and the road data forthe new expressway is not stored in the external storage device 58 ofthe vehicular apparatus 2, the vehicular apparatus 2 does not provide animproper route guidance display based on road data for a road which isnot the new expressway, by erroneous map matching and route searchingusing the road data which is stored in the external storage device 58.

[0255] (2) In this third embodiment, if the communication with theinformation center 1 is disrupted while the vehicle is running on anexpressway (or a toll road) and there remains no route section that isassociated with route guidance information, the computation section 53performs map matching and a route search using the road data of theexternal storage section 58 after the vehicle has exited the expresswayand entered onto an ordinary road (“yes” at step S242 or S244).

[0256] Therefore, in the case where the expressway where thecommunication failure occurred is a new expressway and the road data forthe new expressway is not stored in the external storage device 58 ofthe vehicular apparatus 2, the vehicular apparatus 2 does not performmap matching or a route search using the road data which is stored inthe external storage device 58 until the vehicle exits the expressway.Therefore, proper route guidance display can be started automaticallyafter the vehicle has left the expressway. As a result, no improperroute guidance display is performed in the interval between thecommunication failure and when the vehicle exits the expressway andenters onto an ordinary road.

[0257] (3) In the third embodiment, if map matching does not place thevehicle present position on an ordinary road after the vehicle hasexited the expressway (“no” at step S252), the route guidance operationis finished without performing a route search. This prevents improperroute guidance in the case where the ordinary road that the vehicle hasentered immediately after exiting the expressway is an ordinary road forwhich road data is not stored in the external storage device 58.

[0258] (4) In the embodiment, if the user activates the re-search switchof the input section 55 (“yes” at step S243), the computation section 53performs route guidance by performing a route search using the road datain the external storage device 58. Therefore, even if a communicationfailure has occurred, route guidance can be performed according to theuser's intention by performing map matching and a route search using theroad data for ordinary roads stored in the external storage section 58.

[0259] (5) In the third embodiment, route information used as basis forthe judgement whether the vehicle has exited the expressway and enteredan ordinary road is reception of optical beacon information that istransmitted from existing optical beacons. Therefore, such a judgmentcan be made without the need for installing special facilities.

[0260] (6) In the third embodiment, route information used as basis forthe judgement whether the vehicle has exited the expressway and enteredan ordinary road is the shape of the road travelled by the vehicle. Theshape of each road section of a predetermined length is calculated andit is judged that the vehicle has exited the expressway and entered anordinary road if the calculated road shape coincides with the shape(loop shape) of an interchange. Therefore, whether the vehicle hasentered an ordinary road at an interchange can be judged without theneed for providing a special device.

[0261] (7) In the third embodiment, if it is judged that the vehicle wasnot running on the expressway when the communication failure occurred(“no” at step S250), the computation section 53 prohibits map matchingand a route search using the road data that is stored in the externalstorage section 58 (step S245). Therefore, in the case where the vehiclewas running on a road that is not the expressway (or toll road), such asa new bypass that is provided with optical beacons, when thecommunication failure occurred and the road data for that road is notstored in the external storage device 58 of the vehicular apparatus 2,the vehicular apparatus 2 does not perform improper map matching orimproper route guidance.

[0262] Embodiment 4

[0263] A communication-type car navigation system according to a fourthembodiment of the invention will be described with reference to FIG. 17.The communication-type car navigation system according to the fourthembodiment is different from that according to the second embodimentonly in the manner in which the computation section 53 of the vehicularapparatus 2 operates when the communication with the information center1 has failed. Therefore, for convenience of description, this embodimentwill be described only for that point.

[0264]FIG. 17 is a flowchart showing an operation that is performed bythe computation section 53 of the vehicular apparatus 2 by execution ofthe communication failure countermeasure program 67 when route guidanceinformation for a route ahead of the present position is not availablebecause a communication failure has occurred during route guidance basedon route guidance information transmitted from the information center 1.

[0265] First, the computation section 53 judges whether communicationwith the information center 1 has recovered (step S261). Ifcommunication has not recovered yet (“no” at step S261), the computationsection 53 judges, based on the type data for the road on which thevehicle was travelling immediately before the communication failureoccurred, whether the vehicle was travelling on an ordinary road at thetime of the occurrence (step S262). If the vehicle was travelling on anexpressway (or a toll road) at the time of occurrence of thecommunication failure (“no” at step S262), the computation section 53judges whether optical beacon information has been received (step S263),that is, whether the vehicle has entered onto an ordinary road.

[0266] If no optical beacon information has been received (“no” at stepS263), the computation section 53 judges whether a re-search switch ofthe input section 55 has been activated (step S264). That is, thecomputation section 53 judges whether the user has performed a manualaction to cause the vehicular apparatus 2 to again search for a route tothe destination using the road data of the external storage device 58 byexecuting the route search program 65.

[0267] If the user does not want a re-search (“no” at step S264), thecomputation section 53 judges whether the vehicle has passed aninterchange at which to exit the expressway (step S265). Specifically,as in the case of the third embodiment, the computation section 53calculates curvature of each section, having a predetermined length, ofthe road on which the vehicle is travelling and judges whether thecalculated curvature which represents a road shape coincides withcurvature of a looped interchange that is stored in advance in thememory 54.

[0268] If the computation section 53 judges that the vehicle has notexited the expressway at an interchange to enter an ordinary road (“no”at step S265), the computation section 53 prohibits map matching (stepS266). That is, the computation section 53 prohibits map matching inaccordance with a judgment that the vehicle continues to travel theexpressway after the occurrence of the communication failure and there-search switch of the input section 55 has not been activated. Sincemap matching has been prohibited, the process goes to step S261 withoutagain searching for a route to the destination. At step S261, thecomputation section 53 again judges whether communication with theinformation center 1 has been restored.

[0269] As described above, the computation section 53 of the vehicularapparatus 2 does not perform map matching or a re-search if acommunication failure has occurred while the vehicle was travelling onan expressway and the vehicle is still travelling that expresswaywithout ability to communicate with the information center. As a result,for example, in the case where the expressway where the abnormalcommunication failure occurred is a new expressway and the road data forthe new expressway is not stored in the external storage device 58 ofthe vehicular apparatus 2, the vehicular apparatus 2 does not performimproper display and route guidance wherein the vehicle present positionwould be erroneously indicated to be on an ordinary road for which roaddata is stored in the external storage device 58, rather than on the newexpressway, by map matching.

[0270] If communication with the information center 1 recovers while thevehicle is travelling with map matching and route re-search prohibited(“yes” at step S261), the computation section 53 requests theinformation center 1 to perform a route search (step S267) andtransmits, to the information center 1, information for the vehiclepresent position, travel direction, type of road on which the presentposition is located, destination, transmission road segment length, andsearch condition (step S268).

[0271] The vehicular apparatus 2 receives route guidance informationgenerated by the information center 1 in due course (step S269) and thecomputation section 53 performs map matching based on the received routeguidance information (route guidance data 71) (step S270). From thistime forward, the vehicular apparatus 2 executes route guidance based onthe route guidance information (route guidance data 71) received incommunication with the information center 1.

[0272] On the other hand, if the vehicle was running on an ordinary roadwhen the communication failure occurred (“yes” at step S262) or if thevehicle has exited the expressway and entered an ordinary road (“yes” atstep S263 or S265), the computation section 53 performs map matchingusing the road data in the external storage device 58, judging that theroad data for the road on which the vehicle is now travelling is storedin the external storage device 58 (step S271).

[0273] If the road on which vehicle present position is located is foundby the map matching (“yes” at step S272), the computation section 53searches for a route from the present position to the destination byexecution of the route search program 65 (step S273). From this timeforward, the vehicular apparatus 2 provides route guidance by executingthe route guidance program 61 using the road data of the externalstorage device 58 until communication with the information center 1 isrestored. Conversely, if the road on which the vehicle present positionis located cannot be found by the map matching (“no” at step S272), thecomputation section 53 finishes the execution of the program withoutperforming a route search. That is, the computation section 53 does notperform a route search because of a judgment that the ordinary road onwhich the vehicle is travelling is a road for which road data is notstored in the external storage device 58 and a route search withforcible map matching to an ordinary road for which road data is storedin the external storage device 58 would lead to improper route guidance.

[0274] If the re-search switch of the input section 55 has beenactivated (“yes” at step S264), the computation section 53 performs mapmatching using the road data stored in the external storage device 58according to the user's intention (step S271). From this time forward,the computation section 53 executes steps S272 and S273 as in theabove-described case and finishes the execution of the program.

[0275] The advantages of the above communication-type car navigationsystem according to the fourth embodiment are as follows.

[0276] (1) In this fourth embodiment, if a communication failure occurswhile the vehicle is travelling on an ordinary road with route guidancebased on route guidance information transmitted from the informationcenter 1 (“yes” at step S262), the computation section 53 performs mapmatching and a route search using the road data of the external storagedevice 58.

[0277] Therefore, when a communication failure occurs while the vehicleis travelling on an ordinary road, the vehicular apparatus 2 canimmediately start proper route guidance display.

[0278] (2) In the fourth embodiment, if the communication with theinformation center 1 is lost while the vehicle is travelling on anexpressway (or a toll road) and there is no remaining portion of theroute that is associated with route guidance information, thecomputation section 53 prohibits map matching and route searching usingthe road data of the external storage section 58 as long as the vehiclecontinues to travel on the expressway (“no” at steps S263 and S265).

[0279] Therefore, in the case where the expressway on which thecommunication failure occurred is a new expressway and the road data forthe new expressway is not stored in the external storage device 58 ofthe vehicular apparatus 2, the computation section 53 of the vehicularapparatus 2 does not perform improper route guidance display bysubstituting road data for an ordinary road (not the new expressway),which would result in erroneous map matching, route searching and routeguidance.

[0280] (3) In the fourth embodiment, if the communication with theinformation center 1 is lost while the vehicle is travelling on anexpressway (or a toll road) and there remains no route portion that isassociated with route guidance information, the computation section 53performs map matching and a route search using the road data of theexternal storage section 58 after the vehicle has exited the expresswayand entered an ordinary road (“yes” at step S263 or S265).

[0281] Therefore, if the expressway where the communication failureoccurred is a new expressway and the road data for the new expressway isnot stored in the external storage device 58 of the vehicular apparatus2, the vehicular apparatus 2 performs map matching and a route searchusing the road data stored in the external storage device 58 until thevehicle exits the expressway and enters onto an ordinary road.Therefore, proper route guidance display can be started automaticallyafter the vehicle has entered onto the ordinary road. As a result, noimproper route guidance display is performed in the interval between thecommunication failure and the exit of the vehicle from the expressway.

[0282] (4) In the fourth embodiment, if map matching does not place thevehicle present position on an ordinary road after the vehicle hasexited the expressway, the route guidance operation is then completedwithout performing a route search. This prevents improper route guidancein the case where the ordinary road that the vehicle has enteredimmediately after exiting the expressway is an ordinary road for whichroad data is not stored in the external storage device 58.

[0283]( 5) In the fourth embodiment, if the user activates the re-searchswitch of the input section 55 (“yes” at step S264), the computationsection 53 conducts a route search using the road data of the externalstorage device 58. Therefore, even if a communication failure hasoccurred, route guidance can be performed according to the user'sintention by performing map matching and a route search using the roaddata for ordinary roads stored in the external storage section 58.

[0284] (6) In the fourth embodiment, the route information serving asbasis for a judgement whether the vehicle has exited the expressway andentered an ordinary road is reception of optical beacon information thatis transmitted from existing optical beacons. Therefore, such a judgmentcan be made without the need for installing special facilities.

[0285] (7) In the fourth embodiment, the route information serving asbasis for a judgement whether the vehicle has exited the expressway andentered an ordinary road is the shape of the road on which the vehicleis traveling. The shape of each segment of a predetermined length of theroad on which the vehicle is travelling is calculated and it is judgedthat the vehicle has exited the expressway and entered onto an ordinaryroad if the calculated road shape coincides with the shape (loop shape)of an interchange. Therefore, whether the vehicle has entered onto anordinary road at an interchange can be judged without the need forproviding a special device.

[0286] The third and fourth embodiments of the invention may be modifiedin the following manners:

[0287] In the third and fourth embodiments, the route informationserving as basis for a judgement whether the vehicle has exited anexpressway and entered an ordinary road is optical beacon information orthe shape of the road on which the vehicle is travelling. Alternatively,for example, in the case of a vehicle equipped with an ETC (electronictoll collection) device, whether the vehicle has exited an expresswayand entered an ordinary road may be judged by receiving a signaltransmitted from a tollbooth with an antenna and the ETC system devicewhen the vehicle travels through a tollbooth passage lane (ECT lane).

[0288] In the third and fourth embodiments, a transmission road segmentlength is transmitted from the vehicular apparatus 2 to the informationcenter 1 and the information center 1 generates route guidanceinformation to be transmitted in one transmission attempt based on thereceived transmission road length. Alternatively, the information center1 may determine a transmission road length, generate route guidanceinformation corresponding to that determined road length, and transmitit to the vehicular apparatus 2 in one transmission attempt.

[0289] At step S243 of the third embodiment and step S264 of the fourthembodiment, the user gives a re-search instruction by a manualoperation, that is, activation of the re-search switch of the inputsection 55. Alternatively, the user may give a re-search instruction byvoice using a speech recognition device.

[0290] In the third and fourth embodiments, if the communication withthe information center 1 is lost while the vehicle is running on anexpressway and there remains no route portion associated with routeguidance information, the computation section 53 prohibits map matchingusing the road data of the external storage section 58 (step S245 orS266) as long as the vehicle continues to run on the expressway.

[0291] Instead of prohibiting map matching, the road matching conditionmay made stricter. In the map matching, present position information anda past locus are compared with road shapes on a map and the presentposition marking position is corrected so as to be located on the properroad. For example, if the present position marking position is usuallycorrected so as to be located on the most proper road among those roadswhose deviations are less than X, the map matching condition may be madestricter so that the present position marking position is corrected soas to be located on the most proper road among roads whose deviationsare less than Y.

[0292] According to the present invention, if an expressway where acommunication failure occurred is a new expressway and the road data forthe new expressway is not stored in the road data storing means, there-search means of the vehicular route guidance apparatus does notperform a route search using the road data of the road data storingmeans unless the vehicle exits the expressway and enters onto anordinary road. Therefore, improper route guidance using an ordinary roadfor which road data is stored in the road data storing means, ratherthan the new expressway, is not performed.

[0293] According to the present invention, if a failure occurs incommunication with the information delivery center while the vehicle istravelling on an ordinary road, the re-search means of the vehicularroute guidance apparatus performs a route search using the road data forthe ordinary road that is stored in the road data storing means.Therefore, the vehicular route guidance apparatus can immediately startproper route guidance display.

[0294] Further, according to the invention, the re-search means performsa re-search only if map matching has placed the present position on anordinary road. This can prevent improper route guidance in the casewhere the road data for the ordinary road is not stored in the road datastoring means.

[0295] The invention may be embodied in other specific forms withoutdeparting from the spirit or essential characteristics thereof. Thepresent embodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

INCORPORATION BY REFERENCE

[0296] The teachings of Japanese Application No. 2001-243427, filed Aug.10, 2001, Japanese Application No. 2001-241746 filed Aug. 9, 2001 andJapanese Application No. 2001-245047 filed Aug. 10, 2001 areincorporated by reference herein in their entirety, inclusive of thespecification, claims and drawings.

What is claimed is:
 1. A navigation system comprising: (a) an information center comprising a transmission/reception section for communication, a route search section for searching for a route, based on a present position and destination, and an information generating section for generating major guide point information and guidance information for the route thus found; and (b) a vehicular apparatus comprising a destination setting section for setting a destination, a present position determination section for determining the present position, and a guidance output section for outputting guidance for major guide points and route guidance, and a transmission/reception section for transmitting the set destination and the determined present position to the information center and for receiving the major guide point information and the guidance information from the information center, said guidance output section giving guidance limited to the major guide point information when the transmission/section is unable to receive the guidance information from the information center.
 2. The navigation system according to claim 1, wherein the vehicular apparatus repeatedly updates the present position and transmits the updated present position to the information center, and the information center updates the guidance information based on the updated present position and transmits the updated guidance information to the vehicular apparatus.
 3. An information center comprising: (a) a transmission/reception section for communication; (b) a route search section for searching for a route; and (c) an information generating section for generating major guide point information and guidance information for the found route, wherein the information center searches for the route based on a present position and a destination that are received from a vehicular apparatus and transmits, to the vehicular apparatus, the generated major guide point information and the guidance information.
 4. The information center according to claim 3, wherein the major guide point information includes a name of an interchange of one of an expressway, a toll road, or a high level of a multi-level road.
 5. The information center according to claim 4, wherein if an end, most distant from the present position, of a segment of the found route having a prescribed road length is on an expressway, toll road or a high level of a multi-level road, the information center transmits the name of the interchange to the vehicular apparatus.
 6. A vehicular apparatus for use in a vehicle comprising: (a) a transmission/reception section for communication; (b) a destination setting section for setting a destination; (c) a present position determination section for determining a present position; and (d) a guidance output section for outputting a guidance for major guide points and route guidance wherein the vehicular apparatus transmits the destination and the present position to an information center, receives, from the information center, first major guide point information to be followed by guidance information for a route that has been found by a search based on the destination and the present position, and gives guidance for the major guide points when unable to receive the guidance information.
 7. The vehicular apparatus according to claim 6 wherein: said transmission/reception section receives plural transmissions, each transmission first conveying, within a first period of transmission, the major guide point information for a segment of the found route, followed by the guidance information for the segment of the found route, within a second period of transmission which is significantly longer than the first period of transmission, and wherein the segments of the plural transmissions each have a prescribed length.
 8. The vehicular apparatus according to claim 6, wherein the vehicular apparatus does not give guidance for a major guide point that the vehicle has already passed.
 9. A route guidance system comprising: an information delivery center for generating route guidance information for a recommended route from a present position to a destination in response to a request from a vehicular route guidance apparatus and for transmitting the generated route guidance information to the vehicular route guidance apparatus in a series of transmissions, each transmission providing guidance information for a segment of a recommended route, said route segment having a prescribed length, the information delivery center comprising: search means for searching for the recommended route from the present position to the destination; preliminary route guidance information generating means for generating, if an end of a route segment, for which the preceding transmission provided guidance information, is on an expressway or a toll road, preliminary route guidance information for a preliminary route from the route segment end to an escape position, ahead of the route segment end, on the expressway or toll road; remaining route guidance information generating means for generating remaining route guidance information for a remaining route that is a route segment of the prescribed road length minus the preliminary route; transmitting means for first transmitting the preliminary route guidance information to the vehicular route guidance apparatus and then transmitting the remaining route guidance information to the vehicular route guidance apparatus; and wherein said vehicular route guidance apparatus performs route guidance using the route guidance information transmitted from the information delivery center, and comprises: route guidance means for providing route guidance for the recommended route ahead of the route segment end, when communication with the information delivery center has failed, from the route segment end to an escape location on the expressway or toll road using the preliminary route guidance information that has been received.
 10. The route guidance system according to claim 9, wherein the vehicular route guidance apparatus further comprises: road data storing means in which road data is stored; route search means for searching for a route to the destination using the road data of the road data storing means; and route guidance information generating means for generating route guidance information for guidance along the route that has been found by the route search means.
 11. The route guidance system according to claim 9, wherein the escape location on the expressway or toll road is an escape location that is ahead of and closest to the route segment end.
 12. The route guidance system according to claim 5, wherein the escape location on the expressway or toll road is an interchange, a service area, or a parking area.
 13. An information center for receiving information for a present position and information for a destination from a vehicular route guidance apparatus, for generating route guidance information corresponding to a segment of a recommended route having a prescribed road length, and for transmitting the generated route guidance information to the vehicular route guidance apparatus, the information delivery center comprising: search means for searching for the recommended route from the present position to the destination; preliminary route guidance information generating means for generating, if an end of a route segment which is the subject of preceding transmission of route guidance information is on an expressway or toll road, preliminary route guidance information for a preliminary route from the segment end to an escape location ahead on the expressway or toll road; remaining route guidance information generating means for generating remaining route guidance information for a remaining route that is a segment of the recommended route having the prescribed road length minus the preliminary route; and transmitting means for first transmitting the preliminary route guidance information to the vehicular route guidance apparatus and then transmitting the remaining route guidance information to the vehicular route guidance apparatus.
 14. A vehicular route guidance apparatus for receiving, in succession, transmissions of route guidance information from an information delivery center, each transmission containing guidance information for a segment of a recommended route, said segment having a prescribed road length, and for providing route guidance to a destination using route guidance information provided by the succession of transmissions, said vehicular route guidance apparatus comprising: route guidance information storing means for receiving, from the information delivery center, preliminary route guidance information, generated when an end of a segment, which was the subject of route guidance information of a preceding transmission, is on an expressway or toll road, said preliminary route information corresponding to a preliminary route from the end of the segment to an escape location ahead on the expressway or toll road, and for receiving from the information center remaining route guidance information for a remaining route that is a segment of the recommended route having the prescribed road length minus the preliminary route, and for storing the remaining route guidance information and the preliminary route guidance information; and route guidance means for providing route guidance for the recommended route ahead of the segment end, when a failure occurs in communication with the information delivery center, from the segment end to the escape location on the expressway or toll road using the received preliminary route guidance information.
 15. A route guidance system for a vehicle comprising: an information delivery center for transmitting, to a vehicular route guidance apparatus, route guidance information for route guidance to a destination, said information delivery center comprising: search means for searching for a recommended route to the destination; and transmitting means for transmitting, to the vehicular route guidance apparatus, route guidance information for guidance along the recommended route; and wherein the vehicular route guidance apparatus provides route guidance, based on the route guidance information transmitted from the information delivery center, and comprises: data storage means in which road data is stored; and re-search means for again searching for a route using the stored road data, when a failure has occurred in communication with the information delivery center.
 16. The route guidance system according to claim 15, wherein the re-search means judges, based on route information, whether the vehicle has exited an expressway or toll road.
 17. The route guidance system according to claim 15, wherein the re-search means searches for a route using the stored road data on condition that the failure in communication with the information delivery center occurred while the vehicle was travelling on a road other than an expressway or toll road.
 18. The route guidance system according to claim 15, wherein the re-search means searches for a route again further on condition that the vehicular route guidance apparatus has not received information for the recommended route ahead of the present position of the vehicle.
 19. The route guidance system according to claim 15, further comprising matching means for performing map matching of the vehicle present position when a failure in communication with the information delivery center has occurred and the vehicle has exited an expressway or toll road, and wherein the re-search means searches for a route again on condition that the map matching has placed the present position of the vehicle on a road other than an expressway or toll road.
 20. A method for communication of guidance information between a central information center and plural vehicles each equipped with a vehicular navigation apparatus, said method comprising: transmitting from the vehicular navigation apparatus to the central information center information identifying a present position of a vehicle and a destination; searching, within the central information center, to determine a recommended route from the present vehicle position to the destination; generating guidance information for the recommended route within the central information center; transmitting the generated guidance information, as a series of transmissions, to the vehicular navigation apparatus, each of said transmissions providing guidance information for a segment of the recommended route having a prescribed length, each of said transmissions including a first portion of guidance information of short duration to be utilized for guidance in the event of a failure in communication between the central information center and the vehicular navigation apparatus and a second portion providing more detailed guidance information for the route segment and having a duration significantly longer than that of said first portion. 